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A094518
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Number of pairs (x,y) of divisors of n with x<y such that also x+y is a divisor of n.
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5
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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
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OFFSET
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1,12
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COMMENTS
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LINKS
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EXAMPLE
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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.
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MATHEMATICA
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Table[Count[Subsets[#, {2}], _?(Mod[n, Total@ #] == 0 &)] &@ Divisors@ n, {n, 102}] (* Michael De Vlieger, Sep 10 2018 *)
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PROG
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(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
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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