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A195046 Concentric 15-gonal numbers. 6
0, 1, 15, 31, 60, 91, 135, 181, 240, 301, 375, 451, 540, 631, 735, 841, 960, 1081, 1215, 1351, 1500, 1651, 1815, 1981, 2160, 2341, 2535, 2731, 2940, 3151, 3375, 3601, 3840, 4081, 4335, 4591, 4860, 5131, 5415, 5701, 6000, 6301, 6615, 6931, 7260, 7591 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Harvey P. Dale, 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) = 15*n^2/4+11*((-1)^n-1)/8.

a(0)=0, a(1)=1, a(2)=15, a(3)=31, a(n)=2*a(n-1)-2*a(n-3)+a(n-4) [From Harvey P. Dale, Feb 23 2012]

G.f.: -((x*(1+x*(13+x)))/((-1+x)^3*(1+x))) [From Harvey P. Dale, Feb 23 2012]

MATHEMATICA

Table[15n^2/4+11((-1)^n-1)/8, {n, 0, 50}] (* or *) LinearRecurrence[ {2, 0, -2, 1}, {0, 1, 15, 31}, 50] (* Harvey P. Dale, Feb 23 2012 *)

PROG

(PARI) a(n)=15*n^2/4+11*((-1)^n-1)/8 \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Column 15 of A195040.

Cf. A032527, A032528, A195045, A195047, A195145, A195146.

Sequence in context: A249452 A132757 A045135 * A102955 A041444 A041446

Adjacent sequences:  A195043 A195044 A195045 * A195047 A195048 A195049

KEYWORD

nonn,easy

AUTHOR

Omar E. Pol, Sep 27 2011

EXTENSIONS

Corrected (a(1)=1 added) by Harvey P. Dale, Feb 23 2012

STATUS

approved

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Last modified December 3 10:22 EST 2016. Contains 278699 sequences.