OFFSET
1,6
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..10000
Hùng Việt Chu, Nurettin Irmak, Steven J. Miller, László Szalay, and Sindy Xin Zhang, Schreier Multisets and the s-step Fibonacci Sequences, arXiv:2304.05409 [math.CO], 2023. See also Integers (2024) Vol. 24A, Art. No. A7, p. 4.
FORMULA
G.f.: Sum_{n>=0} x^(n*(n+1)) / (1-x)^n.
EXAMPLE
a(11)=7 because we have: 11, 8+3, 3+8, 7+4, 4+7, 6+5 and 5+6.
MAPLE
G:=sum(x^(k^2+k)/(1-x)^k, k=0..20): Gser:=series(G, x=0, 67): seq(coeff(Gser, x^n), n=1..65); # Emeric Deutsch, Mar 29 2005
MATHEMATICA
nmax = 60; Rest[CoefficientList[Series[Sum[x^(k*(k+1))/(1-x)^k, {k, 1, Sqrt[nmax] + 1}], {x, 0, nmax}], x]] (* Vaclav Kotesovec, Nov 11 2018 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Sep 27 2004
EXTENSIONS
More terms from Emeric Deutsch, Mar 29 2005
STATUS
approved