A176767 - OEIS

%I #14 Apr 03 2024 17:14:21

%S 2401,1,2401,343,49,823543,16807,7,16807,49,96889010407,117649,

%T 13841287201,13841287201,11398895185373143,4747561509943,16807,117649,

%U 11398895185373143,1977326743,13841287201,3909821048582988049

%N Smallest power of 7 whose decimal expansion contains n.

%C This is to 7 as A176763 is to 3 and as A030001 is to 2.

%H Paolo Xausa, <a href="/A176767/b176767.txt">Table of n, a(n) for n = 0..10000</a>

%F a(n) = MIN{A000420(i) such that n in decimal representation is a substring of A000420(i)}.

%F a(n) = 7^A062524(n). - _Michel Marcus_, Sep 30 2014

%e a(1) = 1 because 7^0 = 1 has "1" as a substring (not a proper substring, though).

%e a(2) = 2401 because 7^4 = 2401 has "2" as a substring.

%e a(3) = 343 because 7^3 = 343 has "3" as a substring.

%t A176767[n_] := Block[{k = -1}, While[StringFreeQ[IntegerString[7^++k], IntegerString[n]]]; 7^k]; Array[A176767, 50, 0] (* _Paolo Xausa_, Apr 03 2024 *)

%Y Cf. A000420, A030001, A176763, A176764-A176773.

%K base,easy,nonn

%O 0,1

%A _Jonathan Vos Post_, Apr 25 2010

%E More terms from _Sean A. Irvine_ and _Jon E. Schoenfield_, May 05 2010

%E Extended to a(0) by _M. F. Hasler_, Oct 03 2014