OFFSET
1,2
COMMENTS
By A238448, a(10) <= 244178.
EXAMPLE
2^7 = 128 contains the 2-digit substring "12". Thus a(2) = 7.
PROG
(Python)
def a(n):
..for k in range(1, 10**5):
....for i in range(10):
......s = ''
......for j in range(i, i+n):
........dig=j%10
........s+=str(dig)
......if str(2**k).find(s) > -1:
........return k
n=1
while n < 10:
..print(a(n))
..n+=1
CROSSREFS
KEYWORD
nonn,more,hard,base
AUTHOR
Derek Orr, May 31 2014
EXTENSIONS
a(10)-a(13) from Hiroaki Yamanouchi, Sep 26 2014
STATUS
approved