0,5

Also number of partitions of n with positive crank (n>1), cf. A064391. - Vladeta Jovovic (vladeta(AT)eunet.rs), Sep 30 2001

G. E. Andrews, The reasonable and unreasonable effectiveness of number theory in statistical mechanics, pp. 21-34 of S. A. Burr, ed., The Unreasonable Effectiveness of Number Theory, Proc. Sympos. Appl. Math., 46 (1992). Amer. Math. Soc.

G. E. Andrews, Three-quadrant Ferrers graphs, Indian J. Math., 42 (No. 1, 2000), 1-7.

F. C. Auluck, On some new types of partitions associated with generalized Ferrers graphs. Proc. Cambridge Philos. Soc. 47, (1951), 679-686.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

E. M. Wright, Stacks, III, Quart. J. Math. Oxford, 23 (1972), 153-158.

T. D. Noe, Table of n, a(n) for n = 0..1000

Erich Friedman, Illustration of initial terms

S. Plouffe, Approximations de S\'{e}ries G\'{e}n\'{e}ratrices et Quelques Conjectures, Dissertation, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.

S. Plouffe, 1031 Generating Functions and Conjectures, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.

G.f.: (Sum_{k>0} -(-1)^k x^(k(k+1)/2))/(Product_{k>0} (1-x^k)).

For a(6)=5 we have the following stacks:

.x... ..x.. ...x. .xx.

xxxxx xxxxx xxxxx xxxx xxxxxx

A001522:=(1-z-z**2+z**3-z**6-2*z**7+2*z**5+z**10+z**8)/(1+z)/(z**4+z**3-1)/(z-1)\ **3; [Conjectured by S. Plouffe in his 1992 dissertation.]

(PARI) a(n)=if(n<1, 0, polcoeff(sum(k=1, (sqrt(1+8*n)-1)\2, -(-1)^k*x^((k+k^2)/2))/eta(x+x*O(x^n)), n))

a(n) = (A000041(n)-A064410(n))/2.

Cf. A000041, A059776, A001523, A001524.

Sequence in context: A096778 A102108 A105780 this_sequence A054405 A155167 A116634

Adjacent sequences: A001519 A001520 A001521 this_sequence A001523 A001524 A001525

nonn,easy,nice

N. J. A. Sloane (njas(AT)research.att.com).