A135901 - OEIS

%I #2 Mar 30 2012 18:37:08

%S 1,2,4,7,12,18,26,36,47,60,75,92,111,132,154,178,204,232,262,294,328,

%T 364,402,442,484,527,572,619,668,719,772,827,884,943,1004,1067,1132,

%U 1199,1268,1339,1412,1487,1564,1643,1724,1807,1892,1978,2066,2156,2248

%N Number of terms in row n of irregular triangle A135879 for n>=0.

%F G.f.: A(x) = (1+x^2)/(1-x)^3 - [Sum_{n>=1} x^b(n)]/(1-x)^2, where b(n) = (2^(n+1) + 6*n + 3 + (-1)^n)/12.

%e A(x) = (1+x^2)/(1-x)^3 - [x+x^2+x^3+x^5+x^8+x^14+x^25+x^47+x^90+x^176+...]/(1-x)^2.

%o (PARI) {a(n)=polcoeff((1+x^2)/(1-x+x*O(x^n))^3 - sum(k=1,#binary(n)+2,x^((2^(k+1)+6*k+3+(-1)^k)/12))/(1-x +x*O(x^n) )^2,n)}

%Y Cf. A135879.

%K nonn

%O 0,2

%A _Paul D. Hanna_, Dec 16 2007