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A064762 a(n) = 21*n^2. 5
0, 21, 84, 189, 336, 525, 756, 1029, 1344, 1701, 2100, 2541, 3024, 3549, 4116, 4725, 5376, 6069, 6804, 7581, 8400, 9261, 10164, 11109, 12096, 13125, 14196, 15309, 16464, 17661, 18900, 20181, 21504, 22869, 24276, 25725, 27216, 28749 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Number of edges in a complete 7-partite graph of order 7n, K_n,n,n,n,n,n,n.

LINKS

Table of n, a(n) for n=0..37.

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

FORMULA

a(n) = 42*n+a(n-1)-21 for n>0, a(0)=0. - Vincenzo Librandi, Aug 07 2010

a(n) = 21*A000290(n) = 7*A033428(n) = 3*A033582(n). - Omar E. Pol, Jul 03 2014

a(n) = t(7*n) - 7*t(n), where t(i) = i*(i+k)/2 for any k. Special case (k=1): a(n) = A000217(7*n) - 7*A000217(n). - Bruno Berselli, Aug 31 2017

MATHEMATICA

21 Range[0, 50]^2 (* Wesley Ivan Hurt, Jul 04 2014 *)

LinearRecurrence[{3, -3, 1}, {0, 21, 84}, 40] (* Harvey P. Dale, Jul 29 2019 *)

PROG

(MAGMA) [21*n^2 : n in [0..50]]; // Wesley Ivan Hurt, Jul 04 2014

(PARI) a(n)=21*n^2 \\ Charles R Greathouse IV, Jun 17 2017

CROSSREFS

Cf. A000217, A000290, A033428, A033581, A033583.

Similar sequences are listed in A244630.

Sequence in context: A195961 A190023 A071397 * A104676 A143244 A041856

Adjacent sequences:  A064759 A064760 A064761 * A064763 A064764 A064765

KEYWORD

nonn,easy

AUTHOR

Roberto E. Martinez II, Oct 18 2001

STATUS

approved

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Last modified October 23 23:51 EDT 2019. Contains 328379 sequences. (Running on oeis4.)