A292931 Numbers n such that the sum of digits of 3^n (A004166) is divisible by 7.

25, 26, 30, 32, 47, 58, 79, 81, 87, 89, 102, 123, 141, 144, 145, 151, 164, 176, 178, 193, 201, 227, 239, 242, 257, 264, 282, 289, 300, 306, 319, 324, 329, 335, 336, 338, 348, 351, 358, 365, 395, 403, 437, 441, 450, 460, 468, 484, 489, 492, 495, 517, 518, 541, 542, 544, 554, 555, 563, 565, 570

Offset

1,1

Links

Chai Wah Wu, Table of n, a(n) for n = 1..10000

Mathematics StackExchange, Is sum of digits of 3^1000 divisible by 7?

Example

a(3) = 30 is in the sequence because 3^30 = 205891132094649 has sum of digits 63, which is divisible by 7.

Maple

select(n -> convert(convert(3^n, base, 10), `+`) mod 7 = 0, [$1..1000]);

Mathematica

Select[Range[600], Divisible[Total[IntegerDigits[3^#]], 7]&] (* Harvey P. Dale, Mar 01 2018 *)

Prog

(PARI) isok(n) = !(sumdigits(3^n) % 7); \\ Michel Marcus, Sep 27 2017
(Python)
from __future__ import division
A292931_list = [n for n in range(1000) if not sum(int(d) for d in str(3**n)) % 7] # Chai Wah Wu, Sep 28 2017

Crossrefs

Cf. A004166.

Sequence in context: A340271 A003996 A132415 * A374910 A067810 A111168

Adjacent sequences: A292928 A292929 A292930 * A292932 A292933 A292934

Keyword

nonn,base

Author

Robert Israel, Sep 27 2017

Status

approved