OFFSET
0,2
COMMENTS
Sequence found by reading the line from 0, in the direction 0, 13, ..., in the square spiral whose vertices are the generalized 15-gonal numbers.
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (3,-3,1).
FORMULA
a(n) = 26*n^2 - 13*n = 13*A000384(n).
a(n) = a(n-1) + 52*n - 39, a(0)=0. - Vincenzo Librandi, Oct 03 2011
PROG
(Magma) [13*n*(2*n-1): n in [0..50]]; // Vincenzo Librandi, Oct 03 2011
(PARI) a(n)=13*n*(2*n-1) \\ Charles R Greathouse IV, Jun 17 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Oct 02 2011
STATUS
approved