A242046 Least integer k > n + 1 such that n^2 + (n + 1)^2 + k^2 is prime.

2, 6, 4, 6, 24, 14, 8, 12, 16, 24, 24, 14, 14, 24, 16, 20, 42, 20, 26, 54, 30, 26, 30, 28, 26, 54, 42, 38, 42, 34, 40, 48, 38, 36, 36, 44, 48, 102, 42, 46, 54, 44, 50, 48, 60, 54, 66, 50, 54, 54, 54, 54, 54, 56, 64, 84, 58, 62, 84, 64, 66, 78, 64, 66, 84, 74

Offset: 0

Author

Zak Seidov, Aug 24 2014

Keywords

• nonn

Comments

If n is in A027863 then a(n) = n + 2, otherwise a(n) > n + 2. All terms are even. Corresponding primes are 5, 41, 29, 61, 617, ...

Links

• Jens Kruse Andersen, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A027863.

Programs

Mathematica

lk[n_]:=Module[{k=n+2,c=n^2+(n+1)^2},While[!PrimeQ[c+k^2],k++];k]; Array[ lk,70,0] (* Harvey P. Dale, Aug 06 2015 *)

PARI

a(n)=k=n+2; while(!isprime(n^2+(n+1)^2+k^2), k++); k
vector(100,n,a(n-1)) \\ Jens Kruse Andersen, Aug 26 2014

Extensions

Corrected and extended by Jens Kruse Andersen, Aug 26 2014