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
FORMULA
a(n) = 42*n+a(n-1)-21 for n>0, a(0)=0. - Vincenzo Librandi, Aug 07 2010
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
KEYWORD
nonn,easy
AUTHOR
Roberto E. Martinez II, Oct 18 2001
STATUS
approved