A089912 a(n) gives sum of number of common unitary divisors of n and m, where m runs from 1 to n.

1, 3, 4, 5, 6, 11, 8, 9, 10, 16, 12, 18, 14, 21, 23, 17, 18, 26, 20, 28, 30, 31, 24, 33, 26, 36, 28, 37, 30, 57, 32, 33, 45, 46, 47, 45, 38, 51, 52, 51, 42, 77, 44, 55, 58, 61, 48, 62, 50, 66, 67, 64, 54, 71, 70, 68, 74, 76, 60, 100, 62, 81, 77, 65, 82, 113, 68, 82, 89, 118, 72

Offset: 1

Author

Naohiro Nomoto, Jan 11 2004

Keywords

• easy
• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A034444, A034448.

Programs

Mathematica

udiv[n_] := Select[Divisors[n], GCD[#, n/#]==1 &]; a[n_] := Module[{d = udiv[n]}, Sum[Length[Intersection[d, udiv[k]]], {k,1,n}]]; Array[a, 100] (* Amiram Eldar, Aug 10 2019 *)

PARI

a(n) = {sdivn = Set(); fordiv(n, d, if (gcd(d, n/d) == 1, sdivn = setunion(sdivn, Set(d)))); s = 0; for (m=1, n, sdivm = Set(); fordiv(m, d, if (gcd(d, m/d) == 1, sdivm = setunion(sdivm, Set(d)))); s += length(setintersect(sdivn, sdivm));); return (s);} \\ Michel Marcus, Jul 15 2013