A001748 a(n) = 3 * prime(n).

6, 9, 15, 21, 33, 39, 51, 57, 69, 87, 93, 111, 123, 129, 141, 159, 177, 183, 201, 213, 219, 237, 249, 267, 291, 303, 309, 321, 327, 339, 381, 393, 411, 417, 447, 453, 471, 489, 501, 519, 537, 543, 573, 579, 591, 597, 633, 669, 681, 687, 699, 717, 723, 753

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• easy

Comments

Semiprimes divisible by 3. - Jianing Song, Oct 02 2022

Links

• Paolo P. Lava, Table of n, a(n) for n = 1..20000
• Eric Weisstein's World of Mathematics, Skeleton

Crossrefs

Subsequence of A001358.

Cf. A000040, A100484, A253046, A164023, A164024, A179545, A253046.

Programs

Haskell

a001748 = (* 3) . a000040  -- Reinhard Zumkeller, Dec 26 2014

Magma

[3*p: p in PrimesUpTo(300)]; // Vincenzo Librandi, Mar 26 2014

Mathematica

Prime[Range[22]]*3 (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 *)

PARI

3*primes(22) \\ Charles R Greathouse IV, May 19 2011

Formula

A164023(a(n)) = A164024(a(n)) = A000040(n). - Reinhard Zumkeller, Aug 09 2009

a(n) = 3*A000040(n). - Omar E. Pol, Jan 31 2012

A253046(a(n)) < a(n). - Reinhard Zumkeller, Dec 26 2014