A280953 - OEIS

%I #11 Dec 28 2018 19:38:12

%S 1,1,1,1,1,1,1,2,2,2,2,2,2,2,3,3,3,3,3,4,4,5,5,5,5,5,6,6,7,7,7,7,7,8,

%T 8,9,9,10,11,11,12,12,13,13,14,15,15,16,16,17,17,18,19,19,20,20,22,23,

%U 24,25,25,27,27,29,30,31,32,32,34,34,36,37,38,39,40,43,44,46,47,48,50,51,54,55,57,58,59

%N Expansion of Product_{k>=0} 1/(1 - x^(3*k*(k+1)+1)).

%C Number of partitions of n into centered hexagonal numbers (A003215).

%H Alois P. Heinz, <a href="/A280953/b280953.txt">Table of n, a(n) for n = 0..20000</a>

%H M. Bernstein and N. J. A. Sloane, <a href="http://arXiv.org/abs/math.CO/0205301">Some canonical sequences of integers</a>, Linear Alg. Applications, 226-228 (1995), 57-72; erratum 320 (2000), 210. [Link to arXiv version]

%H M. Bernstein and N. J. A. Sloane, <a href="/A003633/a003633_1.pdf">Some canonical sequences of integers</a>, Linear Alg. Applications, 226-228 (1995), 57-72; erratum 320 (2000), 210. [Link to Lin. Alg. Applic. version together with omitted figures]

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HexNumber.html">Hex Number</a>

%H <a href="/index/Ce#CENTRALCUBE">Index entries for sequences related to centered polygonal numbers</a>

%H <a href="/index/Par#partN">Index entries for related partition-counting sequences</a>

%F G.f.: Product_{k>=0} 1/(1 - x^(3*k*(k+1)+1)).

%e a(14) = 3 because we have [7, 7], [7, 1, 1, 1, 1, 1, 1, 1] and [1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1].

%p h:= proc(n) option remember; `if`(n<0, 0, (t->

%p       `if`(3*t*(t+1)+1>n, t-1, t))(1+h(n-1)))

%p     end:

%p b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<0, 0,

%p       b(n, i-1)+(t-> b(n-t, min(i, h(n-t))))(3*i*(i+1)+1)))

%p     end:

%p a:= n-> b(n, h(n)):

%p seq(a(n), n=0..100);  # _Alois P. Heinz_, Dec 28 2018

%t nmax = 86; CoefficientList[Series[Product[1/(1 - x^(3 k (k + 1) + 1)), {k, 0, nmax}], {x, 0, nmax}], x]

%Y Cf. A003215, A278949, A279222, A280950, A280951, A280952.

%K nonn

%O 0,8

%A _Ilya Gutkovskiy_, Jan 11 2017