OFFSET
1,2
COMMENTS
Exponential reversion of A000217 (triangular numbers).
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..200
FORMULA
a(n) ~ -(-1)^n * n^(n-1) / (2^(1/4) * (sqrt(2)-1)^(n - 1/2) * exp(n*(sqrt(2)-1))). - Vaclav Kotesovec, Apr 21 2020
MATHEMATICA
nmax = 18; CoefficientList[InverseSeries[Series[Exp[x] (x + x^2/2), {x, 0, nmax}], x], x] Range[0, nmax]! // Rest
PROG
(PARI) seq(n)= Vec(serlaplace(serreverse(sum(k=1, n, (k*(k+1)/2)*x^k/k!) + O(x*x^n)))); \\ Michel Marcus, Apr 21 2020
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Apr 20 2020
STATUS
approved