OFFSET
0,3
COMMENTS
Sequence found by reading the line from 0, in the direction 0, 9, ... and the line from 1, in the direction 1, 18, ..., in the square spiral whose vertices are the triangular numbers A000217.
LINKS
FORMULA
Array read by rows: row n gives 8*n^2 + n, 8*(n+1)^2 - 7*(n+1).
G.f.: -x*(7*x+1)/((x-1)^3*(x+1)). - Colin Barker, Oct 16 2012
a(n) = 2*n^2 + (7/2)*n + (3/4)*((-1)^n-1). - Sean A. Irvine, Jul 14 2022
EXAMPLE
Array begins:
0, 1;
9, 18;
34, 51;
75, 100;
...
CROSSREFS
KEYWORD
nonn,easy,tabf
AUTHOR
Omar E. Pol, May 03 2008
STATUS
approved