A242553 - OEIS

%I #7 Jan 12 2020 19:57:04

%S 1,1,10,1,6,5,12,13,16,3,24,7,2,3,8,9,4,17,4,7,2,3,20,7,8,19,10,3,10,

%T 19,14,17,32,11,8,25,6,25,40,7,10,43,16,5,68,7,30,5,8,19,58,17,26,17,

%U 2,11,10,3,4,49,6,71,22,15,14,47,30,9,2,19,6,19,6,5,28,13,2

%N Least number k such that n^8+k^8 is prime.

%C If a(n) = 1, then n is in A006314.

%e 10^8+1^8 = 100000001 is not prime. 10^8+2^8 = 100000256 is not prime. 10^8+3^8 = 100006561 is prime. Thus, a(10) = 3.

%t lnk[n_]:=Module[{c=n^8,k=1},While[CompositeQ[c+k^8],k++];k]; Array[lnk,80] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Jan 12 2020 *)

%o (Python)

%o import sympy

%o from sympy import isprime

%o def a(n):

%o ..for k in range(10**4):

%o ....if isprime(n**8+k**8):

%o ......return k

%o n = 1

%o while n < 100:

%o ..print(a(n))

%o ..n += 1

%o (PARI) a(n)=for(k=1,10^3,if(ispseudoprime(n^8+k^8),return(k)));

%o n=1;while(n<100,print(a(n));n+=1)

%Y Cf. A069003, A006314.

%K nonn

%O 1,3

%A _Derek Orr_, May 17 2014