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A064762
a(n) = 21*n^2.
6
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
OFFSET
0,2
COMMENTS
Number of edges in a complete 7-partite graph of order 7n, K_n,n,n,n,n,n,n.
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
Similar sequences are listed in A244630.
Sequence in context: A359024 A190023 A071397 * A104676 A143244 A041856
KEYWORD
nonn,easy
AUTHOR
STATUS
approved