saved some chars
algorithmshark
• 8.5k
• 2
• 29
• 53

# J - 3535 32 char

"Prompt the user" is the bane of every J golfer. There go 8 ofall my hard-earned characters!

p:(n,n)#:i.&n,+/~(*1&p~p:)i.n=:".1!:1]1


Explained:

• ".1!:1]1 - Read in a string (1!:1) from input (file handle 1) and convert it to a number (".).
• p:i.n=: - Assign this number to the variable n, and then take the list of integers less thanfirst n.
• (*1&p:) - Multiply each number by 1 if it is prime, and 0 if it isn't primes.
• +/~ - Make an addition table, n wide and n high.
• i.&n, - Turn the table into a single list, and then find the index of the first occurrence of n, which exists if Goldbach's conjecture is true.
• p:(n,n)#: - Retrieve the row and column from the index, and take the corresponding primes.

Usage:

   p:(n,n)#:i.&n,+/~(*1&p~p:)i.n=:".1!:1]1
666
5 661
p:(n,n)#:i.&n,+/~(*1&p~p:)i.n=:".1!:1]1
1024
3 1021


Had the prompt not been a requirement, here's the 27a 25 character verb:

(,~#~p:@#:]i.~[:~&,+/~@(*1&p:)p:@i.)

algorithmshark
• 8.5k
• 2
• 29
• 53

# J - 35 char

"Prompt the user" is the bane of every J golfer. There go 8 of my characters!

(n,n)#:i.&n,+/~(*1&p:)i.n=:".1!:1]1


Explained:

• ".1!:1]1 - Read in a string (1!:1) from input (file handle 1) and convert it to a number (".).
• i.n=: - Assign this number to the variable n, and then take the list of integers less than n.
• (*1&p:) - Multiply each number by 1 if it is prime, and 0 if it isn't.
• +/~ - Make an addition table, n wide and n high.
• i.&n, - Turn the table into a single list, and then find the index of the first occurrence of n, which exists if Goldbach's conjecture is true.
• (n,n)#: - Retrieve the row and column from the index.

Usage:

   (n,n)#:i.&n,+/~(*1&p:)i.n=:".1!:1]1
666
5 661
(n,n)#:i.&n,+/~(*1&p:)i.n=:".1!:1]1
1024
3 1021


Had the prompt not been a requirement, here's the 27 character verb:

(,~#:]i.~[:,+/~@(*1&p:)@i.)