OFFSET
0,2
COMMENTS
Number of triples {A, B, C} where 1 <= A <= B <= C <= n+1 and gcd(C-B, B-A) = 1. E.g., for n=2, we have the 5 triples {1, 1, 2}, {1, 2, 2}, {2, 2, 3}, {2, 3, 3}, and {1, 2, 3}. - Griffin N. Macris, May 21 2016
LINKS
Griffin N. Macris, Table of n, a(n) for n = 0..99999
FORMULA
a(n) ~ n^2*(3+n) / Pi^2. - Griffin N. Macris, May 21 2016
MATHEMATICA
Table[Sum[Sum[EulerPhi[j], {j, i}] + 1, {i, n}], {n, 0, 30}] (* Birkas Gyorgy, Feb 19 2011 *)
Table[n + Sum[ EulerPhi[ j], {i, n}, {j, i}], {n, 0, 30}] (* Robert G. Wilson v, Feb 12 2015 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved