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A195048 Concentric 19-gonal numbers. 8
0, 1, 19, 39, 76, 115, 171, 229, 304, 381, 475, 571, 684, 799, 931, 1065, 1216, 1369, 1539, 1711, 1900, 2091, 2299, 2509, 2736, 2965, 3211, 3459, 3724, 3991, 4275, 4561, 4864, 5169, 5491, 5815, 6156, 6499, 6859, 7221, 7600, 7981, 8379, 8779, 9196 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Also concentric enneadecagonal numbers.

LINKS

Ivan Panchenko, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (2,0,-2,1).

FORMULA

a(n) = 19*n^2/4+15*((-1)^n-1)/8.

a(n) = 2*a(n-1)-2*a(n-3)+a(n-4). G.f.: x*(1+17*x+x^2)/((1-x)^3*(1+x)). - Colin Barker, Sep 16 2012

MATHEMATICA

LinearRecurrence[{2, 0, -2, 1}, {0, 1, 19, 39}, 50] (* Harvey P. Dale, May 17 2016 *)

PROG

(PARI) a(n)=19*n^2/4+15*((-1)^n-1)/8 \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Column 19 of A195040.

Cf. A032527, A032528, A195047, A195147, A195148, A195049.

Sequence in context: A079044 A258016 A217731 * A041714 A041716 A041718

Adjacent sequences:  A195045 A195046 A195047 * A195049 A195050 A195051

KEYWORD

nonn,easy

AUTHOR

Omar E. Pol, Sep 27 2011

STATUS

approved

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Last modified February 17 21:12 EST 2018. Contains 299297 sequences. (Running on oeis4.)