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A158186 a(n) = 10*n^2 - 7*n + 1. 3
1, 4, 27, 70, 133, 216, 319, 442, 585, 748, 931, 1134, 1357, 1600, 1863, 2146, 2449, 2772, 3115, 3478, 3861, 4264, 4687, 5130, 5593, 6076, 6579, 7102, 7645, 8208, 8791, 9394, 10017, 10660, 11323, 12006, 12709, 13432, 14175, 14938, 15721, 16524, 17347 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Sequence found by reading the segment (1, 4) together with the line (one of the diagonal axes) from 4, in the direction 4, 27, ..., in the square spiral whose vertices are the generalized heptagonal numbers A085787. - Omar E. Pol, Sep 10 2011

LINKS

Table of n, a(n) for n=0..42.

Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

FORMULA

a(n) = (2*n-1)*(5*n-1).

a(n) = A033571(n) - A008596(n) = A010010(n) - A033571(n).

G.f.: (1+x+18*x^2)/(1-x)^3. - Jaume Oliver Lafont, Mar 27 2009

a(n) = a(n-1) + 20*n - 17 (with a(0)=1). - Vincenzo Librandi, Dec 03 2010

PROG

(PARI) a(n)=10*n^2-7*n+1 \\ Charles R Greathouse IV, Jun 17 2017

CROSSREFS

Sequence in context: A175701 A227866 A180576 * A272858 A272818 A272859

Adjacent sequences:  A158183 A158184 A158185 * A158187 A158188 A158189

KEYWORD

nonn,easy

AUTHOR

Reinhard Zumkeller, Mar 13 2009

EXTENSIONS

Typo in definition corrected by Reinhard Zumkeller, Dec 03 2009

STATUS

approved

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Last modified June 17 07:31 EDT 2019. Contains 324183 sequences. (Running on oeis4.)