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

1, 113, 106, 259, 304, 85, 212, 135, 158, 47, 62, 985, 84, 47, 518, 485, 178, 169, 106, 27, 88, 139, 632, 47, 44, 643, 20, 209, 606, 1529, 32, 31, 1094, 139, 754, 647, 38, 37, 262, 69, 94, 631, 90, 25, 38, 195, 10, 277, 232, 187, 554, 189, 10, 47, 216, 131, 1132, 173, 390

Offset: 1

Author

Derek Orr, May 17 2014

Keywords

• nonn

Comments

If a(n) = 1, then n is in A056994.

Crossrefs

Cf. A069003, A056994.

Programs

Mathematica

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 *)

PARI

a(n)=for(k=1,10^4,if(ispseudoprime(n^128+k^128),return(k)));
n=1;while(n<100,print(a(n));n+=1)

Python

import sympy
from sympy import isprime
def a(n):
    for k in range(10**4):
        if isprime(n**128+k**128):
            return k
n = 1
while n < 100:
    print(a(n))
    n += 1