OFFSET
0,2
LINKS
David A. Corneth, Table of n, a(n) for n = 0..9999
FORMULA
EXAMPLE
For n = 2 the a(2) = 12 pairs are (2,1), (2,0), (2,-1), (1,1), (1,0), (1,-1), (1,-2), (0,0), (0,-1), (0,-2), (-1,-1), and (-1,-2). - Danny Rorabaugh, Apr 05 2016
MATHEMATICA
a[n_]:=2Sum[Length[Divisors[k]], {k, 1, n}]+Floor[Sqrt[n]]+2n+1
PROG
(PARI) a(n) = 2*sum(k=1, n, numdiv(k)) + sqrtint(n) + 2*n + 1; \\ Michel Marcus, Apr 05 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Lorenz H. Menke, Jr., Mar 15 2016
STATUS
approved