OFFSET
0,2
COMMENTS
Number of edges in a complete 8-partite graph of order 8n, K_n,n,n,n,n,n,n,n.
Sequence found by reading the line from 0, in the direction 0, 28,..., in the square spiral whose vertices are the generalized 16-gonal numbers. - Omar E. Pol, Jul 03 2014
LINKS
FORMULA
a(n) = 56*n+a(n-1)-28 (with a(0)=0). - Vincenzo Librandi, Aug 07 2010
a(n) = 28*A000290(n) = 14*A001105(n) = 7*A016742(n) = 4*A033582(n) = 2*A144555(n). - Omar E. Pol, Jul 03 2014
G.f.: 28*x*(1+x)/(1-x)^3. - Vincenzo Librandi, Mar 30 2015
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3). - Vincenzo Librandi, Mar 30 2015
a(n) = t(8*n) - 8*t(n), where t(i) = i*(i+k)/2 for any k. Special case (k=1): a(n) = A000217(8*n) - 8*A000217(n). - Bruno Berselli, Aug 31 2017
MATHEMATICA
CoefficientList[Series[28 x (1 + x) / (1 - x)^3, {x, 0, 40}], x] (* Vincenzo Librandi, Mar 30 2015 *)
PROG
(Magma) [28*n^2: n in [0..40]] /* or */ I:=[0, 28, 112]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+Self(n-3): n in [1..40]]; // Vincenzo Librandi, Mar 30 2015
(PARI) a(n)=28*n^2 \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Roberto E. Martinez II, Oct 18 2001
STATUS
approved