A261558 Euclid numbers (A006862) of the form 3*(i*i + i*j + j*j + i + j) + 1 where i and j are integers.

7, 31, 211, 2311, 510511, 6469693231, 200560490131, 304250263527211, 117288381359406970983271, 7858321551080267055879091, 40729680599249024150621323471, 232862364358497360900063316880507363071, 279734996817854936178276161872067809674997231

Offset: 1

Author

Altug Alkan, Nov 18 2015

Keywords

• nonn

Comments

Intersection of A006862 and A202822.

Examples

			a(1) = 7 because 7 = 2*3 + 1 = 3*(1^2 + 1*0 + 0^2 + 1 + 0) + 1.
		

Links

• Eric Weisstein's World of Mathematics, Euclid Number

Crossrefs

Cf. A003136, A006862, A202822.

Programs

PARI

a(n) = prod(k=1, n, prime(k)) + 1;
isA(n) = if( n<1 || (n%3 == 0), 0, 0 != sumdiv( n, d, kronecker( -3, d)));
for(n=0, 30, if(isA(a(n)), print1(a(n), ", ")))