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A195041 Concentric heptagonal numbers. 8
0, 1, 7, 15, 28, 43, 63, 85, 112, 141, 175, 211, 252, 295, 343, 393, 448, 505, 567, 631, 700, 771, 847, 925, 1008, 1093, 1183, 1275, 1372, 1471, 1575, 1681, 1792, 1905, 2023, 2143, 2268, 2395, 2527, 2661, 2800, 2941, 3087, 3235, 3388, 3543 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

A033582 and A069127 interleaved.

Partial sums of A047336. - Reinhard Zumkeller, Jan 07 2012

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..10000

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

FORMULA

a(n) = 7*n^2/4+3*((-1)^n-1)/8.

G.f.: -x*(1+5*x+x^2) / ( (1+x)*(x-1)^3 ). a(n)+a(n+1) = A069099(n+1). - R. J. Mathar, Sep 28 2011

a(n) = n^2 + floor(3*n^2/4). - Bruno Berselli, Aug 08 2013

PROG

(MAGMA) [7*n^2/4+3*((-1)^n-1)/8: n in [0..50]]; // Vincenzo Librandi, Sep 29 2011

(Haskell)

a195041 n = a195041_list !! n

a195041_list = scanl (+) 0 a047336_list

-- Reinhard Zumkeller, Jan 07 2012

(PARI) a(n)=7*n^2\4 \\ Charles R Greathouse IV, Oct 07 2015

CROSSREFS

Column 7 of A195040.

Cf. A032527, A032528, A077221, A195042.

Sequence in context: A239934 A193553 A274090 * A229462 A006188 A198589

Adjacent sequences:  A195038 A195039 A195040 * A195042 A195043 A195044

KEYWORD

nonn,easy

AUTHOR

Omar E. Pol, Sep 27 2011

STATUS

approved

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Last modified August 20 13:35 EDT 2017. Contains 290835 sequences.