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A135901 Number of terms in row n of irregular triangle A135879 for n>=0. 1
1, 2, 4, 7, 12, 18, 26, 36, 47, 60, 75, 92, 111, 132, 154, 178, 204, 232, 262, 294, 328, 364, 402, 442, 484, 527, 572, 619, 668, 719, 772, 827, 884, 943, 1004, 1067, 1132, 1199, 1268, 1339, 1412, 1487, 1564, 1643, 1724, 1807, 1892, 1978, 2066, 2156, 2248 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..50.

FORMULA

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.

EXAMPLE

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.

PROG

(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)}

CROSSREFS

Cf. A135879.

Sequence in context: A227590 A267529 A005521 * A124197 A011909 A065962

Adjacent sequences:  A135898 A135899 A135900 * A135902 A135903 A135904

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Dec 16 2007

STATUS

approved

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Last modified September 21 16:31 EDT 2021. Contains 347598 sequences. (Running on oeis4.)