A243017 - OEIS

A243017

Least number k > 0 such that k*n/(k+n) and k*n/(k-n) are integers or 0 if no such k exists.

0, 0, 6, 12, 0, 3, 0, 24, 18, 15, 0, 4, 0, 0, 10, 48, 0, 9, 0, 30, 28, 0, 0, 8, 0, 0, 54, 21, 0, 15, 0, 96, 66, 0, 210, 12, 0, 0, 78, 24, 0, 21, 0, 132, 30, 0, 0, 16, 0, 75, 102, 156, 0, 27, 66, 42, 114, 0, 0, 12, 0, 0, 84, 192, 0, 33, 0, 204, 138, 105, 0, 24, 0, 0, 50, 228

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OFFSET

1,3

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10080

EXAMPLE

3*6/(6+3) = 2 and 3*6/(6-3) = 9 are both integers. Thus a(3) = 6.

PROG

(PARI) a(n)=for(k=1, n*(n+1), if(k!=n, if((k*n)%(k+n)==0&&(k*n)%(k-n)==0, return(k))))

n=1; while(n<100, print1(a(n), ", "); n+=1)

CROSSREFS

Cf. A243045, A243046, A243047 (positions of 0's), A360120 (their characteristic function).