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A005476 a(n) = n*(5*n - 1)/2. 20
0, 2, 9, 21, 38, 60, 87, 119, 156, 198, 245, 297, 354, 416, 483, 555, 632, 714, 801, 893, 990, 1092, 1199, 1311, 1428, 1550, 1677, 1809, 1946, 2088, 2235, 2387, 2544, 2706, 2873, 3045, 3222, 3404, 3591 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..38.

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

FORMULA

a(n) = C(5*n,2)/5 for n>=0. - Zerinvary Lajos, Jan 02 2007

a(n) = A033991(n) - A000326(n). - Zerinvary Lajos, Jun 11 2007

a(n) = a(n-1) + 5*n - 3 for n>0, a(0)=0. - Vincenzo Librandi, Nov 18 2010

a(n) = A000217(n) + A000384(n) = A000290(n) + A000326(n). - Omar E. Pol, Jan 11 2013

a(n) = A130520(5*n+1). - Philippe Deléham, Mar 26 2013

a(n) = A033994(n) - A033994(n-1). - J. M. Bergot, Jun 12 2013

From Bruno Berselli, Oct 17 2016: (Start)

G.f.: x*(2 + 3*x)/(1 - x)^3.

a(n) = A000217(3*n-1) - A000217(2*n-1). (End)

MAPLE

[seq(binomial(5*n, 2)/5, n=0..38)]; # Zerinvary Lajos, Jan 02 2007

MATHEMATICA

Table[n (5 n - 1)/2, {n, 0, 40}] (* Vladimir Joseph Stephan Orlovsky, Oct 25 2008 *)

PROG

(PARI) a(n)=n*(5*n-1)/2 \\ Charles R Greathouse IV, Sep 24 2015

CROSSREFS

Cf. A000217, A005475, A033994.

Cf. numbers of the form n*(n*k-k+4))/2 listed in A226488.

Cf. similar sequences listed in A022288.

Sequence in context: A002888 A041963 A298912 * A316430 A131476 A023549

Adjacent sequences:  A005473 A005474 A005475 * A005477 A005478 A005479

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified December 16 15:11 EST 2018. Contains 318172 sequences. (Running on oeis4.)