A239012 - OEIS

%I #26 Jan 22 2020 14:44:51

%S 0,2,3,6,10,11,19,35,127,131,175,207,1235,2470,2651,1241310,1922910,

%T 471056338,1001431598,1720335627,4203146094,5353516238,21838571507,

%U 25770284079,40822793867

%N Exponents m such that the decimal expansion of 7^m exhibits its first zero from the right later than any previous exponent.

%C Assume that a zero precedes all decimal expansions. This will take care of those cases in A030703.

%C Inspired by the seqfan list discussion Re: "possible sequence", beginning with David Wilson 7:57 PM Mar 06 2014 and continued by _M. F. Hasler_, _Allan C. Wechsler_ and _Franklin T. Adams-Watters_.

%t f[n_] := Position[ Reverse@ Join[{0}, IntegerDigits[ PowerMod[7, n, 10^500]]], 0, 1, 1][[1, 1]]; k = mx = 0; lst = {}; While[k < 500000001, c = f[k]; If[c > mx, mx = c; AppendTo[ lst, k]; Print@ k]; k++]; lst

%Y Cf. A000420, A030703, A020665, A031142, A239008, A239009, A239010, A239011, A239013, A239014, A239015.

%K nonn,base,more

%O 1,2

%A _Charles R Greathouse IV_ and _Robert G. Wilson v_, Mar 14 2014

%E a(19)-a(22) from _Bert Dobbelaere_, Jan 21 2019

%E a(23)-a(25) from _Chai Wah Wu_, Jan 15 2020