A333326 Odd numbers k such that k is the product of 2 numbers greater than one, in two or more ways.

45, 63, 75, 81, 99, 105, 117, 135, 147, 153, 165, 171, 175, 189, 195, 207, 225, 231, 243, 245, 255, 261, 273, 275, 279, 285, 297, 315, 325, 333, 345, 351, 357, 363, 369, 375, 385, 387, 399, 405, 423, 425, 429, 435, 441, 455, 459, 465, 475

Offset

1,1

Comments

Odd numbers that are not 1, a prime, the square or cube of a prime, or the product of two primes. - Robert Israel, Mar 19 2020

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

For n=2 the a(2) = 63 because 63 = 3 * 21 and 7 * 9.

Maple

select(t -> numtheory:-tau(t) >= 5, [seq(i, i=3..1000, 2)]); # Robert Israel, Mar 19 2020

Mathematica

Select[2 * Range[250] + 1, DivisorSigma[0, #] > 4 &] (* Amiram Eldar, Mar 15 2020 *)

Prog

(PARI) forcomposite(n=4, 475, if(n%2 == 0, next()); if(numdiv(n) >= 5, print1(n, ", "))); \\ Joerg Arndt, Mar 15 2020

Crossrefs

Cf. A005408, A058080, A226025.

Sequence in context: A140277 A242263 A242264 * A077646 A230577 A336555

Adjacent sequences: A333323 A333324 A333325 * A333327 A333328 A333329

Keyword

nonn

Author

Dimitris Valianatos, Mar 15 2020

Status

approved