A267697 Numbers with 7 odd divisors.

729, 1458, 2916, 5832, 11664, 15625, 23328, 31250, 46656, 62500, 93312, 117649, 125000, 186624, 235298, 250000, 373248, 470596, 500000, 746496, 941192, 1000000, 1492992, 1771561, 1882384, 2000000, 2985984, 3543122, 3764768, 4000000, 4826809, 5971968, 7086244, 7529536, 8000000, 9653618

Offset

1,1

Comments

Positive integers that have exactly seven odd divisors.

Numbers n such that the symmetric representation of sigma(n) has 7 subparts. - Omar E. Pol, Dec 28 2016

Numbers that can be formed in exactly 6 ways by summing sequences of 2 or more consecutive positive integers. - Julie Jones, Aug 13 2018

Numbers of the form p^6 * 2^k where p is an odd prime. - David A. Corneth, Aug 14 2018

Links

David A. Corneth, Table of n, a(n) for n = 1..10000

Formula

A001227(a(n)) = 7.

Prog

(PARI) isok(n) = sumdiv(n, d, (d%2)) == 7; \\ Michel Marcus, Apr 03 2016
(PARI) upto(n) = {my(res = List()); forprime(p = 3, sqrtnint(n, 6), listput(res, p^6)); q = #res; for(i = 1, q, odd = res[i]; for(j = 1, logint(n \ odd, 2), listput(res, odd <<= 1))); listsort(res); res} \\ David A. Corneth, Aug 14 2018

Crossrefs

Column 7 of A266531.

Cf. A001227, A030516, A038547, A236104, A237593, A279387.

Numbers with k odd divisors (k = 1..10): A000079, A038550, A072502, apparently A131651, A267696, A230577, this sequence, A267891, A267892, A267893.

Sequence in context: A046319 A119710 A043455 * A232925 A255112 A255627

Adjacent sequences: A267694 A267695 A267696 * A267698 A267699 A267700

Keyword

nonn,easy

Author

Omar E. Pol, Apr 03 2016

Extensions

More terms from Michel Marcus, Apr 03 2016

Status

approved