A049304 - OEIS

%I #28 Feb 02 2025 01:56:33

%S 6,7,9,13,21,22,23,29,39,40,42,44,45,48,53,55,56,60,63,64,65,67,68,69,

%T 70,73,74,75,76,77,79,82,83,87,89,92,93,94,98,105,107,127,129,131,134,

%U 137,143,147,152,163,165,167,174,179,184,189,197,224,226,227,234,240

%N Numbers k such that k is a substring of 6^k.

%H David A. Corneth, <a href="/A049304/b049304.txt">Table of n, a(n) for n = 1..10000</a>

%e 9 is in the sequence because 6^9 = 10077696 contains 9 as a substring. - _David A. Corneth_, Aug 13 2021

%t Select[Range[250],SequenceCount[IntegerDigits[6^#],IntegerDigits[#]]>0&] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Aug 03 2018 *)

%o (Python)

%o def ok(n): return str(n) in str(6**n)

%o print(list(filter(ok, range(241)))) # _Michael S. Branicky_, Aug 13 2021

%o (PARI) is(n) = { my(digs6n, digsn, streak, i, j); digs6n = digits(6^n); digsn = digits(n); for(i = 1, #digs6n + 1 - #digsn, streak = 0; for(j = 1, #digsn, if(digs6n[i + j - 1] == digsn[j], streak++ , next(2) ) ); if(streak == #digsn, return(1) ) ); 0 } \\ _David A. Corneth_, Aug 13 2021

%Y Cf. A000400, A032740, A049301, A049302, A049303, A049305, A049306, A049307.

%K nonn,base,easy,changed

%O 1,1

%A _David W. Wilson_