A094518 Number of pairs (x,y) of divisors of n with x

0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 2, 0, 1, 0, 0, 0, 5, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 6, 0, 0, 0, 2, 0, 3, 0, 0, 0, 0, 0, 7, 0, 0, 0, 0, 0, 3, 0, 1, 0, 0, 0, 12, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 11, 0, 0, 0, 0, 0, 2, 0, 3, 0, 0, 0, 9, 0, 0, 0, 0, 0, 9, 0, 0, 0, 0, 0, 9, 0, 0, 0, 2, 0, 2

Offset: 1

Author

Reinhard Zumkeller, May 06 2004

Keywords

• nonn

Comments

a(A094519(n)) > 0, a(A094520(n)) = 0.

a(A097370(n)) = n and a(m) <> n for m < A097370(n).

Examples

			n=30 with divisor set {1,2,3,5,6,10,15,30}: a(30)=4, as 1<2 & 3=1+2, 1<5 & 6=1+5, 2<3 & 5=2+3 and 5<10 & 15=5+10.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537

Crossrefs

Cf. A091009.

Programs

Mathematica

Table[Count[Subsets[#, {2}], ?(Mod[n, Total@ #] == 0 &)] &@ Divisors@ n, {n, 102}] (* _Michael De Vlieger, Sep 10 2018 *)

PARI

A094518(n) = if(1==n,0,my(d=divisors(n),c=0); for(i=1,(#d-1),for(j=(i+1),#d,if(!(n%(d[i]+d[j])),c++))); (c)); \\ Antti Karttunen, Sep 10 2018