A043305 - OEIS

1, 3, 6, 7, 15, 21, 28, 31, 33, 42, 69, 84, 91, 93, 105, 127, 135, 141, 186, 217, 231, 270, 273, 285, 381, 420, 465, 483, 496, 546, 573, 651, 762, 775, 819, 861, 868, 889, 924, 945, 987, 1023, 1149, 1185, 1302, 1365, 1419, 1485, 1488, 1561, 1638, 1743, 1890

COMMENTS

After 1, a subsequence of A216782. If both x and y are terms and gcd(x, y) = 1, then x*y is also present. - Antti Karttunen, Mar 20 2023

MATHEMATICA

Select[Range[2000], IntegerQ[Log[2, Numerator[Total[1/Divisors[#]]]]]&] (* Harvey P. Dale, Nov 29 2014 *)

PROG

(PARI) isok(n) = (ispower(num = numerator(sigma(n)/n), , &s) && (s == 2)) || (num == 2) || (num == 1); \\ Michel Marcus, Nov 21 2013

(PARI) isA043305(n) = { n=sigma(n)/gcd(sigma(n), n); !bitand(n, n-1); }; \\ Antti Karttunen, Mar 20 2023