1,1

a(n) are the primes that equal the sum of the r-th powers of the first s triangular numbers. For first 5 listed terms the corresponding pairs of integers r and s are {r,s} = { {4,5}, {12,13}, {26,29}, {27,33}, {90,5} }. There are also known terms corresponding to {r,s} = { {35,285}, {144,5}, {141,37}, {179,13} } which are too large to include.

Cf. A019434 = Fermat primes: primes of form 2^(2^n) + 1.

Adjacent sequences: A128876 A128877 A128878 this_sequence A128880 A128881 A128882

Sequence in context: A106774 A075671 A112015 this_sequence A089009 A093791 A135430

nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), May 08 2007