OFFSET
0,1
COMMENTS
Consider a spiral similar to the spiral described in A239660 but instead of having four quadrants on the square grid the new spiral has six wedges on the triangular grid. A "diamond" formed by two adjacent triangles has area 1. a(n) is the number of diamonds (or the area) added in the fourth wedge after n turns. The interesting fact is that for n >> 1 the geometric pattern in the fourth wedge of the spiral is similar to the geometric pattern of the second wedge but it is different from the other wedges.
MATHEMATICA
Table[DivisorSigma[1, 6*n + 4], {n, 0, 60}] (* Amiram Eldar, Sep 09 2023 *)
PROG
(PARI) a(n) = sigma(6*n+4); \\ Michel Marcus, Sep 08 2023
CROSSREFS
KEYWORD
nonn,easy,less
AUTHOR
Omar E. Pol, Sep 07 2023
STATUS
approved