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Multiples of 3 in A247665 in order of appearance.
2

%I #7 Oct 12 2014 21:18:06

%S 9,15,27,57,81,177,243,393,579,729,849,1257,2187,4197,4143,5853,6561,

%T 17817,17781,19683,56157,59049,104289,104277,154509

%N Multiples of 3 in A247665 in order of appearance.

%C 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.

%e Table showing index where multiples of 3 appear, the multiple of 3, and the number of different prime factors of that term:

%e 6 9 1

%e 13 15 2

%e 28 27 1

%e 57 57 2

%e 115 81 1

%e 231 177 2

%e 463 243 1

%e 927 393 2

%e 1855 579 2

%e 3711 729 1

%e 7423 849 2

%e 14847 1257 2

%e 29695 2187 1

%e 59391 4197 2

%e 118783 4143 2

%e 237567 5853 2

%e 475135 6561 1

%e 950271 17817 2

%e 1900543 17781 2

%e 3801087 19683 1

%e 7602175 56157 2

%e 15204351 59049 1

%e 30408703 104289 2

%e 60817407 104277 2

%e 121634815 154509 2

%Y Cf. A247665, A248379 (multiples of 2).

%K nonn,more

%O 1,1

%A _Russ Cox_ and _N. J. A. Sloane_, Oct 12 2014