A287661 Smallest odd number with exactly n nonprime divisors.

1, 9, 27, 45, 105, 135, 225, 405, 315, 675, 177147, 1155, 945, 3375, 1575, 6075, 2835, 10125, 18225, 3465, 4725, 30375, 50625, 11025, 25515, 91125, 14175, 10395, 23625, 273375, 1476225, 17325, 33075, 759375, 50031545098999707, 31185, 70875, 1366875, 127575

Offset

1,2

Links

Giovanni Resta, Table of n, a(n) for n = 1..1000

Eric Weisstein's World of Mathematics, Divisor

Formula

A033273(a(n)) = n.

Example

a(5) = 105 because 105 has 8 divisors {1, 3, 5, 7, 15, 21, 35, 105} among which 5 are nonprime {1, 15, 21, 35, 105} and 105 is the smallest odd with exactly 5 nonprime divisors.

Crossrefs

Cf. A001221, A002110, A003680, A005179, A033273, A038547, A055079, A070826.

Sequence in context: A031088 A020156 A342869 * A062231 A133636 A369564

Adjacent sequences: A287658 A287659 A287660 * A287662 A287663 A287664

Keyword

nonn

Author

Ilya Gutkovskiy, May 29 2017

Extensions

a(35)-a(39) from Giovanni Resta, May 31 2017

Status

approved