OFFSET
0,1
COMMENTS
For an origin of this sequence, see the triangular spiral illustrated in the Links section.
First bisection gives A117625 (without the initial term).
LINKS
Bruno Berselli, Table of n, a(n) for n = 0..1000
Bruno Berselli, Illustration of initial terms.
Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
FORMULA
MATHEMATICA
LinearRecurrence[{1, 2, -2, -1, 1}, {2, 4, 12, 18, 31}, 60] (* Harvey P. Dale, Jun 15 2022 *)
PROG
(PARI) for(n=0, 50, print1((6*n*(3*n+7)+(2*n+13)*(-1)^n+3)/16+1", "));
(Magma) [(6*n*(3*n+7)+(2*n+13)*(-1)^n+3)/16+1: n in [0..50]];
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Bruno Berselli, Oct 25 2011
STATUS
approved