login
This site is supported by donations to The OEIS Foundation.

 

Logo

Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A089912 a(n) gives sum of number of common unitary divisors of n and m, where m runs from 1 to n. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

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 *)

PROG

(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

CROSSREFS

Cf. A034444, A034448.

Sequence in context: A271821 A261459 A215249 * A047425 A048989 A299299

Adjacent sequences:  A089909 A089910 A089911 * A089913 A089914 A089915

KEYWORD

easy,nonn

AUTHOR

Naohiro Nomoto, Jan 11 2004

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)