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A016161 Expansion of 1/((1-5x)(1-7x)). 5
1, 12, 109, 888, 6841, 51012, 372709, 2687088, 19200241, 136354812, 964249309, 6798573288, 47834153641, 336059778612, 2358521965909, 16540171339488, 115933787267041, 812299450322412, 5689910849522509 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Also, this is the number of incongruent integer-edged Heron triangles whose circumdiameter is the product of n distinct primes each of shape 4k + 1. Cf. A003462, A109021. - R. K. Guy, Jan 31 2007

LINKS

Table of n, a(n) for n=0..18.

Index entries for linear recurrences with constant coefficients, signature (12,-35).

FORMULA

a(n) = (7^(n+1)-5^(n+1))/2 = A081200(n+1). Binomial transform of A080962. - R. J. Mathar, Sep 18 2008

a(n)=7*a(n-1)+5^n. [From Vincenzo Librandi, Feb 09 2011]

PROG

(PARI) Vec(1/((1-5*x)*(1-7*x))+O(x^99)) \\ Charles R Greathouse IV, Sep 24 2012

CROSSREFS

Sequence in context: A011999 A128877 A085797 * A081200 A016214 A037581

Adjacent sequences:  A016158 A016159 A016160 * A016162 A016163 A016164

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified March 23 21:31 EDT 2017. Contains 283985 sequences.