A053850 Odd numbers divisible by a square > 1.

9, 25, 27, 45, 49, 63, 75, 81, 99, 117, 121, 125, 135, 147, 153, 169, 171, 175, 189, 207, 225, 243, 245, 261, 275, 279, 289, 297, 315, 325, 333, 343, 351, 361, 363, 369, 375, 387, 405, 423, 425, 441, 459, 475, 477, 495, 507, 513, 525, 529, 531, 539, 549, 567

Offset: 1

Author

Enoch Haga, Mar 28 2000

Keywords

• easy
• nonn

Comments

Odd n such that sum(k=1,n-1,floor(k^3/n)) is different from (1/4)*(n-2)*(n^2-1) (equality holds for n prime as well as for "1" union "A024556" ). - Benoit Cloitre, Dec 08 2002

Odd nonsquarefree numbers, odd terms of A013929. - Zak Seidov, Aug 16 2006

The asymptotic density of this sequence is 1/2 - 4/Pi^2 = 0.094715... - Amiram Eldar, Nov 21 2020

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000
• Eric Weisstein's World of Mathematics, Prime Sums.

Crossrefs

Cf. A078837, A013929, A024556.

Programs

Mathematica

Select[Range[1, 500, 2], !SquareFreeQ[#] &] (* Amiram Eldar, Nov 21 2020 *)

PARI

lista(nn) = {forstep(n=1, nn, 2, if (! issquarefree(n), print1(n, ", ")));} \\ Michel Marcus, Jun 06 2014