OFFSET
0,2
COMMENTS
a(n) is the denominator of sigma(m)/m when m is A243512(n), the least integer i such that sigma(i)/i = (k+n)/k for some k.
LINKS
Michel Marcus, Table of n, a(n) for n = 0..629
EXAMPLE
MATHEMATICA
f[n_] := Block[{r = DivisorSigma[1, n]/n}, Numerator[r] - Denominator@ r]; Denominator[DivisorSigma[-1, #]] & /@ Table[i = 1; While[f@ i != n, i++]; i, {n, 0, 62}] (* Michael De Vlieger, Sep 10 2015 *)
PROG
(PARI) oksk(n, k) = {my(ab = sigma(k, -1)); numerator(ab) == denominator(ab)+n; }
a(n) = {my(k=1); while(!oksk(n, k), k++); denominator(sigma(k, -1)); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Sep 10 2015
STATUS
approved