OFFSET
1,1
COMMENTS
The decimal expansion of 2^k ends in 7776 iff k == 40 (mod 500), so the sequence is infinite. - Jon E. Schoenfield, Oct 14 2019
Conjecture: if n > 30536, then a(n) = n + 3623. - Chai Wah Wu, Oct 26 2019
LINKS
Chai Wah Wu, Table of n, a(n) for n = 1..10000
EXAMPLE
16777216 = 2^24.
MAPLE
q:= n-> searchtext("777", cat(2^n))>0:
select(q, [$1..600])[]; # Alois P. Heinz, Oct 26 2019
MATHEMATICA
aQ[n_] := SequenceCount[IntegerDigits[2^n], {7, 7, 7}] > 0; Select[Range[660], aQ] (* Amiram Eldar, Oct 26 2019 *)
PROG
(Python)
A328375_list = [k for k in range(1000) if '777' in str(2**k)] # Chai Wah Wu, Oct 26 2019
CROSSREFS
KEYWORD
nonn,easy,base
AUTHOR
Eder Vanzei, Oct 14 2019
STATUS
approved