cp's OEIS Frontend

A242557 Least number k such that n^128+k^128 is prime.

%I A242557 #10 Jun 18 2020 09:17:14
%S A242557 1,113,106,259,304,85,212,135,158,47,62,985,84,47,518,485,178,169,106,
%T A242557 27,88,139,632,47,44,643,20,209,606,1529,32,31,1094,139,754,647,38,37,
%U A242557 262,69,94,631,90,25,38,195,10,277,232,187,554,189,10,47,216,131,1132,173,390
%N A242557 Least number k such that n^128+k^128 is prime.
%C A242557 If a(n) = 1, then n is in A056994.
%t A242557 lnk[n_]:=Module[{c=n^128,k},k=If[EvenQ[c],1,2];While[!PrimeQ[c+ k^128],k = k+2];k]; Join[{1},Array[lnk,60,2]] (* _Harvey P. Dale_, Mar 17 2015 *)
%o A242557 (Python)
%o A242557 import sympy
%o A242557 from sympy import isprime
%o A242557 def a(n):
%o A242557     for k in range(10**4):
%o A242557         if isprime(n**128+k**128):
%o A242557             return k
%o A242557 n = 1
%o A242557 while n < 100:
%o A242557     print(a(n))
%o A242557     n += 1
%o A242557 (PARI) a(n)=for(k=1,10^4,if(ispseudoprime(n^128+k^128),return(k)));
%o A242557 n=1;while(n<100,print(a(n));n+=1)
%Y A242557 Cf. A069003, A056994.
%K A242557 nonn
%O A242557 1,2
%A A242557 _Derek Orr_, May 17 2014