A248381 Multiples of 3 in A247665 in order of appearance.

9, 15, 27, 57, 81, 177, 243, 393, 579, 729, 849, 1257, 2187, 4197, 4143, 5853, 6561, 17817, 17781, 19683, 56157, 59049, 104289, 104277, 154509

Offset

1,1

Comments

The initial multiples of 3 occur at positions 6,13,28,57,115,231, ... - conjecturally, for n > 13, A247665(n) is a multiple of 3 iff n = 29*2^k-1, k >= 0.

Links

Table of n, a(n) for n=1..25.

Example

Table showing index where multiples of 3 appear, the multiple of 3, and the number of different prime factors of that term:
6 9 1
13 15 2
28 27 1
57 57 2
115 81 1
231 177 2
463 243 1
927 393 2
1855 579 2
3711 729 1
7423 849 2
14847 1257 2
29695 2187 1
59391 4197 2
118783 4143 2
237567 5853 2
475135 6561 1
950271 17817 2
1900543 17781 2
3801087 19683 1
7602175 56157 2
15204351 59049 1
30408703 104289 2
60817407 104277 2
121634815 154509 2

Crossrefs

Cf. A247665, A248379 (multiples of 2).

Sequence in context: A046353 A340095 A046356 * A060874 A147511 A124580

Adjacent sequences: A248378 A248379 A248380 * A248382 A248383 A248384

Keyword

nonn,more

Author

Russ Cox and N. J. A. Sloane, Oct 12 2014

Status

approved