OFFSET
1,2
COMMENTS
Records of A239972.
Recall that the abundancy index of n is defined as sigma(n)/n with sigma(n) being the sum of divisors of n (A000203). The numerators and denominators of the abundancy index can be found in A017665 and A017666.
It appears that all terms belong to A014567, numbers such that sigma(n) and n are coprime.
Odd terms begin: 1, 3, 7, 21, 27, 63, 93; and no others were found up to 10^7. What is the next odd number, or is 93 the last odd number in the sequence?
LINKS
Michel Marcus, Table of n, a(n) for n = 1..254
Eric Weisstein's World of Mathematics, Abundancy
PROG
(PARI) lista(nn) = {num = 0; den = 0; for (n = 1, nn, ab = sigma(n)/n; nab = numerator(ab); dab = denominator(ab); if ((nab > num) && (dab > den), print1(n, ", "); num = nab; den = dab; ); ); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Mar 30 2014
STATUS
approved