

A292931


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


2



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
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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: A186538 A003996 A132415 * A067810 A111168 A195331
Adjacent sequences: A292928 A292929 A292930 * A292932 A292933 A292934


KEYWORD

nonn,base


AUTHOR

Robert Israel, Sep 27 2017


STATUS

approved



