2,1

a(n) = 2*floor( 1/2 + sqrt(n-1)). - Antonio Esposito (antonio.b.esposito(AT)italtel.it), Jan 21 2002

With a different offset: g.f. = Sum(i=0, inf, 2*x^(i^2+i)/(1-x)). - Ralf Stephan (ralf(AT)ark.in-berlin.de), Mar 11 2003

Cf. A001650, A000194.

Sequence in context: A083551 A080374 A035683 this_sequence A100144 A076222 A098667

Adjacent sequences: A001667 A001668 A001669 this_sequence A001671 A001672 A001673

nonn,easy

njas