OFFSET
0,2
COMMENTS
The square root of the g.f. of this sequence is an integer series (cf. A261594).
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..50
Ville Salo, Decidability and Universality of Quasiminimal Subshifts, arXiv:1411.6644 [math.DS], 2014-2015.
FORMULA
a(n) ~ 2^(n*(n-1)). - Vaclav Kotesovec, Nov 27 2017
EXAMPLE
G.f.: A(x) = 1 + 2*x + 7*x^2 + 80*x^3 + 4381*x^4 + 1069742*x^5 +...
MATHEMATICA
Table[Sum[Binomial[n, k]*2^(2*Binomial[k, 2]), {k, 0, n}], {n, 0, 25}] (* G. C. Greubel, Nov 07 2016 *)
PROG
(PARI) {a(n)=sum(k=0, n, binomial(n, k)*2^(k*(k-1)))}
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Nov 27 2007
STATUS
approved