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A094518 Number of pairs (x,y) of divisors of n with x<y such that also x+y is a divisor of n. 5
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,12

COMMENTS

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

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

LINKS

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

EXAMPLE

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.

MATHEMATICA

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

PROG

(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

CROSSREFS

Cf. A091009.

Sequence in context: A334740 A059484 A035678 * A123074 A095269 A308275

Adjacent sequences:  A094515 A094516 A094517 * A094519 A094520 A094521

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, May 06 2004

STATUS

approved

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Last modified May 19 18:35 EDT 2022. Contains 353847 sequences. (Running on oeis4.)