1,1

a(3) = 17 because 1 + x + x^2 + x^3 + x^5 + x^7 + x^11 + x^13 + x^17 is irreducible over GF(2).

Do[ If[ ToString[ Factor[ 1 + x + Sum[ x^Prime[k], {k, 1, n} ], Modulus -> 2]] == ToString[ 1 + x + Sum[ x^Prime[k], {k, 1, n} ] ], Print[ Prime[ n ] ] ], {n, 1, 250}]

Sequence in context: A149992 A134128 A119254 this_sequence A084528 A149993 A148413

Adjacent sequences: A056676 A056677 A056678 this_sequence A056680 A056681 A056682

nonn

Robert G. Wilson v (rgwv(AT)rgwv.com), Nov 10 2000