

A329174


a(n) is the least positive exponent k such that the decimal expansion of 7^k contains n consecutive zeros.


1



1, 4, 20, 74, 154, 499, 510, 4411, 6984, 33836, 61282, 709339, 1570651
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

0,2


LINKS



EXAMPLE

7^20 = 79792266297612001 is the first power of 7 that has 2 consecutive zeros, so a(2) = 20.
7^74 = 344552147465294110719732986332367243247925798357929806000836849 is the first power of 7 that has 3 consecutive zeros, so a(3) = 74.


MATHEMATICA

Print[1]; zero = {}; Do[zero = zero <> "0"; k = 1; While[StringPosition[ToString[7^k], zero] == {}, k++]; Print[k]; , {n, 1, 10}]


CROSSREFS



KEYWORD

nonn,base,more,hard


AUTHOR



EXTENSIONS



STATUS

approved



