A333817 - OEIS

%I #7 Apr 06 2020 18:23:28

%S 1,0,0,0,0,1,1,0,0,0,1,0,0,0,0,1,1,1,0,0,1,0,0,0,0,1,1,0,0,0,1,0,1,1,

%T 0,1,1,0,0,0,1,0,0,0,0,1,1,1,0,0,1,0,0,1,1,1,1,0,0,0,1,0,1,0,0,1,1,0,

%U 0,0,1,0,0,1,0,1,1,1,0,1,2,0,0,0,0,1,1,0,0,0,1,0,1

%N G.f.: Sum_{k>=1} x^(k*(5*k - 3)/2) / (1 - x^(5*k)).

%C Number of ways to write n as the difference of two heptagonal numbers.

%F G.f.: Sum_{i>=0} Sum_{j>=i} Product_{k=i..j} x^(5*k + 1).

%t nmax = 93; CoefficientList[Series[Sum[x^(k (5 k - 3)/2)/(1 - x^(5 k)), {k, 1, nmax}], {x, 0, nmax}], x] // Rest

%Y Cf. A000566, A001227, A034178, A333815, A333816, A333818.

%K nonn

%O 1,81

%A _Ilya Gutkovskiy_, Apr 06 2020