A243150 Least number k > 0 such that 2^k contains an n-digit long substring of the infinite string "0123456789012345678901234567890123456....".

1, 7, 28, 106, 391, 992, 1178, 7255, 15975, 67143, 333212, 333212, 1641257

Offset

1,2

Comments

By A238448, a(10) <= 244178.

Links

Table of n, a(n) for n=1..13.

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

Cf. A238448.

Sequence in context: A000416 A000417 A200762 * A344206 A026642 A200467

Adjacent sequences: A243147 A243148 A243149 * A243151 A243152 A243153

Keyword

nonn,more,hard,base

Author

Derek Orr, May 31 2014

Extensions

a(10)-a(13) from Hiroaki Yamanouchi, Sep 26 2014

Status

approved