A136652 L.g.f.: A(x) = log( Sum_{n>=0} 2^[n(n-1)/2]*x^n ).

1, 3, 19, 223, 4771, 190023, 14441659, 2130394591, 616038609331, 351153716973303, 395928966997611499, 885010943452285951183, 3928049212346654960720611, 34658088824057172975437120103, 608435145369338712372672919898779, 21266998855813018955669706360248449471

Offset

1,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..80

Example

L.g.f.: A(x) = x + 3*x^2/2 + 19*x^3/3 + 223*x^4/4 + 4771*x^5/5 +...
A(x) = log(1 + x + 2x^2 + 8x^3 + 64x^4 + 1024x^5 +...+ 2^(n(n-1)/2)*x^n +...).

Mathematica

max = 14; s = Log[Sum[2^(k*(k-1)/2)*x^k, {k, 0, max}]] + O[x]^(max+1); CoefficientList[s, x]*Range[0, max] // Rest (* Jean-François Alcover, Sep 03 2017 *)

Prog

(PARI) a(n)=n*polcoeff(log(sum(k=0, n, 2^(k*(k-1)/2)*x^k +x*O(x^n))), n)

Crossrefs

Cf. A136653, A136654.

Sequence in context: A271587 A217906 A166380 * A136504 A003111 A160888

Adjacent sequences: A136649 A136650 A136651 * A136653 A136654 A136655

Keyword

nonn

Author

Paul D. Hanna, Jan 15 2008

Status

approved