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Walking past Grandpa, who seemed to be snoozing, I saw a note in his left hand, with the name of a film I recognized on it. As I sat down opposite him, he opened his eyes.

Me: "What's on your mind Grandpa?"
Grandpa: "The lawn needs a trim, but I'd rather watch the film I've written down on this note in my hand."

Me: "Grandpa, if I can't guess the film, I'll cut the grass - front and back!"
Grandpa: "OK son, I'll give you some clues. It was released in a leap year, and won a prime number of Oscars."

I said the name of the film I'd seen on the piece of paper.

Grandpa smiled, handed it to me and said, "You've a lot to learn son, looks like I'll be watching my film after all."

What film had Grandpa written down, and how was I tricked?

In tribute to DEEM's Grandpa series, which are so enjoyable and interesting.

Tom
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    I'm not an expert on films, but maybe rot13(bayl n cneg bs gur zbivr gvgyr jnf ivfvoyr va tenaqcn'f cvrpr bs cncre. Vg pbhyq or gur ivfvoyr cneg vf gur gvgyr bs nabgure zbivr juvpu nyfb jnf eryrnfrq va n yrnc lrne naq jba n cevzr ahzore bs Bfpnef) – melfnt Apr 19 '20 at 17:43
  • I was going down the path of thinking that rot13(gur gvgyr vf n lrne gung ybbxf yvxr vg fcryyf fbzrguvat hcfvqr qbja, be ivpr irefn, ohg V pna'g svaq bar). – shoover Apr 19 '20 at 17:49
  • @Tom: doh, my brain hiccuped. I thought it said the release years were prime. But they're leap years. – smci Apr 20 '20 at 07:49
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    Thanks for the attribution @Tom. This is the kind of thing Grandpa loves to do. Been there done that. :) – DrD Apr 20 '20 at 18:47

2 Answers2

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You guessed

Argo (2012), which won three Oscars.

Grandpa's film was

Fargo (1996), which won two Oscars.

How you were tricked:

Grandpa was awake all along, and in order to trick you he deliberately concealed the first letter of the film with his thumb?

Credit to

melfnt, who guessed the exact mechanism in the comments!

Jafe
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It was the film TITANIC made in 1952, awarded 1 Oscar, that Grampa wanted to watch. You read TITANIC and assumed he wanted to see the one made in 1996, awarded 11 Oscars.

zurgeg
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Vassilis Parassidis
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    It looks like Titanic (maybe made in 1952) was released in 1953. The prime is in an older edition of Hardy's Pure Mathematics. – Tom Apr 19 '20 at 19:14
  • ^ Edsger W. Dijkstra – Tom Apr 19 '20 at 19:30
  • @Tom. Hardy expresses an opinion by definition of primes. 1 is a prime. – Vassilis Parassidis Apr 19 '20 at 19:32
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    Technically 1 isn't a prime because 1 and itself are the same number. – merrybot Apr 19 '20 at 19:56
  • @merrybot. Is 2 a prime yes or not. – Vassilis Parassidis Apr 19 '20 at 20:04
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    2 is a prime. 1 isn't. – merrybot Apr 19 '20 at 20:34
  • @merrybot According to Wikipedia the Goldbach conjecture states: Every even number greater than 2 can be expressed as the sum of two primes, so 2+3=5 but 5 is not an even number. In addition to that the sum of two odd numbers make an even number. Also, if you add 1 to any odd number you always obtain an even number. (All numbers integers.) – Vassilis Parassidis Apr 19 '20 at 21:05
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    A prime number is a number greater than 1 that is not the product of any two numbers other than 1 and itself. I know my mathematics. – merrybot Apr 19 '20 at 21:20
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    A prime is an integer with exactly two factors. 1 has a single factor, itself only, and is not prime. "Every even number greater than 2 can be..." means the conjecture applies only to even numbers greater than 2. 5 is not even, and neither 1 nor 2 are greater than 2, so none of Goldbach's conjecture is relevant here and doesn't prove anything to support you. – Nij Apr 20 '20 at 06:25
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    Not to mention the later film was not released in 1996... – Jafe Apr 20 '20 at 06:29
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    @VassilisParassidis Not sure what your point is: the Goldbach conjecture doesn't state that every sum of 2 Primes is an even number. A→B ≠ B→A . Also, as 1 isn't a Prime Number, then the only way to obtain 4 is 2+2. And, we specify "greater than 1", because otherwise 2 has 4 factors (1,2,-1,-2), and the only "prime" number would be -1 (with factors 1 and -1). Perhaps a better description would be "An number whose only integer factor larger than 1 is itself"? – Chronocidal Apr 20 '20 at 08:47
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    What a prime number "is" is a matter of definition, not some deep mathematical fact. Historically, both 1 and 2 have been considered prime and not prime. Defining the primes so that 1 is not a prime but 2 is can be convenient, but it is not universal, nor a provable fact. Nearly every modern mathematician defines the primes so that 1 is not prime (because it makes many theorems easier to state), but there are a few iconoclasts. In any event, the other answer is better, but I like the idea that Grandpa is tricky about his definition of primes (as well as using the same film title twice). – Xander Henderson Apr 20 '20 at 15:55