OFFSET
1,2
COMMENTS
a(n) is equal to n^2 + 1 with predictable regularity; in particular, the values of n for which a(n) does not equal n^2 + 1 are exactly those values n for which 3n is divisible by A269347(3*m) for some m with 1 < m < n. This is in part because 1 + sum{i=1...n}(2i - 1) = n^2 + 1; when computing a(n), each term has this form except when the named condition holds.
For example, a(5) does not equal 5^2 + 1 because 3(5) is divisible by A269347(6).
LINKS
Alec Jones, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A269347(3*n)/3.
PROG
(PARI) lista(nn) = {nn *= 3; va = vector(nn); va[1] = 1; for (n=2, nn, va[n] = sum(k=1, n-1, k*((n % va[k])==0)); ); vector(#va\3, n, va[3*n]/3); } \\ Michel Marcus, Apr 04 2016
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Alec Jones, Apr 04 2016
STATUS
approved