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A243303 Least number k > 0 such that 2^k contains an n-digit long substring of the infinite string "98765432109876543210987654..." 0
1, 5, 25, 78, 161, 341, 1076, 16361, 19383, 56047, 132903, 862935, 862935 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n+1) >= a(n) for all n.

a(10) > 50000.

LINKS

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

EXAMPLE

2^25 = 33554432 contains a 3-digit substring of "98765432109876543210987654..." (in this case, "432"). Since 25 is the lower power to have this property, a(3) = 25.

PROG

(Python)

def Rev(n):

..rev = ''

..for i in str(n):

....rev = i + rev

..return rev

def a(n):

..lst = []

..for b in range(1, 10**n):

....if len(str(2**b)) >= n:

......lst.append(b)

......break

..for k in range(lst[0], 50000):

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

......s = ''

......s += str(i)

......for j in range(i+1, i+n):

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

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

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

........return k

n = 1

while n < 100:

..print(a(n), end=', ')

..n += 1

CROSSREFS

Cf. A243150.

Sequence in context: A056374 A301912 A171272 * A238449 A062989 A122679

Adjacent sequences:  A243300 A243301 A243302 * A243304 A243305 A243306

KEYWORD

nonn,base,hard,more

AUTHOR

Derek Orr, Jun 04 2014

EXTENSIONS

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

STATUS

approved

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Last modified May 25 15:24 EDT 2019. Contains 323572 sequences. (Running on oeis4.)