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A243150 Least number k > 0 such that 2^k contains an n-digit long substring of the infinite string "0123456789012345678901234567890123456....". 1

%I

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

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

%C By A238448, a(10) <= 244178.

%e 2^7 = 128 contains the 2-digit substring "12". Thus a(2) = 7.

%o (Python)

%o def a(n):

%o ..for k in range(1,10**5):

%o ....for i in range(10):

%o ......s = ''

%o ......for j in range(i,i+n):

%o ........dig=j%10

%o ........s+=str(dig)

%o ......if str(2**k).find(s) > -1:

%o ........return k

%o n=1

%o while n < 10:

%o ..print(a(n))

%o ..n+=1

%Y Cf. A238448.

%K nonn,more,hard,base

%O 1,2

%A _Derek Orr_, May 31 2014

%E a(10)-a(13) from _Hiroaki Yamanouchi_, Sep 26 2014

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Last modified September 29 17:14 EDT 2020. Contains 337432 sequences. (Running on oeis4.)