cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A078124 Second column, M(n+1,1) for n>=0, of infinite lower triangular matrix M defined in A078122.

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%I A078124 #7 Mar 30 2012 18:36:32
%S A078124 1,3,12,93,1632,68457,7112055,1879090014,1287814075131,
%T A078124 2325758241901161,11213788533232011006,145939965725683888932081,
%U A078124 5174322925070232320838406581,503750821963423009552527526376232
%N A078124 Second column, M(n+1,1) for n>=0, of infinite lower triangular matrix M defined in A078122.
%H A078124 Alois P. Heinz, <a href="/A078124/b078124.txt">Table of n, a(n) for n = 0..40</a>
%F A078124 The partitions of 2*3^n into powers of 3, or, the coefficient of x^(2*3^n) in 1/Product_{j=0..inf}(1-x^(3^j)) (conjecture).
%e A078124 a(1)=3 since the coefficient of x^6 in 1/Product_{j=0..inf}(1-x^(3^j)) = 1 + x + x^2 + 2x^3 + 2x^4 + 2x^5 + 3x^6 + ... is 3.
%t A078124 m[i_, j_] := m[i, j]=If[j==0||i==j, 1, m3[i-1, j-1]]; m2[i_, j_] := m2[i, j]=Sum[m[i, k]m[k, j], {k, j, i}]; m3[i_, j_] := m3[i, j]=Sum[m[i, k]m2[k, j], {k, j, i}]; a[n_] := m[n+1, 1]
%Y A078124 Cf. A078121, A078122 (matrix shift when cubed), A078123, A078125.
%K A078124 nonn
%O A078124 0,2
%A A078124 _Paul D. Hanna_, Nov 18 2002