A004167 - OEIS

%I #24 Feb 19 2021 13:44:37

%S 1,3,9,72,18,342,927,7812,1656,38691,94095,741771,144135,3234951,

%T 9692874,70984341,12764034,361041921,984024783,7641622611,1044876843,

%U 30235306401,90695018313,72887134149,184635924282,344906882748,9238285681452,7894847955267

%N Powers of 3 written backwards.

%C From a(2) onwards, all terms are divisible by 9. - _Alonso del Arte_, Apr 04 2014

%H Alois P. Heinz, <a href="/A004167/b004167.txt">Table of n, a(n) for n = 0..1000</a>

%F a(n) = A004086(A000244(n)). - _Michel Marcus_, Apr 05 2014

%e a(5) = 342 since 3^5 = 243.

%p a:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||(3^n)):

%p seq(a(n), n=0..50);  # _Alois P. Heinz_, Apr 09 2015

%t Table[FromDigits[Reverse[IntegerDigits[3^n]]], {n, 0, 26}] (* _Alonso del Arte_, Apr 04 2014 *)

%o (Python)

%o def A004167(n):

%o     return int(str(3**n)[::-1]) # _Chai Wah Wu_, Feb 19 2021

%Y The following are parallel families: A000079 (2^n), A004094 (2^n reversed), A028909 (2^n sorted up), A028910 (2^n sorted down), A036447 (double and reverse), A057615 (double and sort up), A263451 (double and sort down); A000244 (3^n), A004167 (3^n reversed), A321540 (3^n sorted up), A321539 (3^n sorted down), A163632 (triple and reverse), A321542 (triple and sort up), A321541 (triple and sort down).

%K nonn,base,easy

%O 0,2

%A _N. J. A. Sloane_

%E More terms from _Eric M. Schmidt_, Apr 04 2014