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A244849 Least number k > 0 such that 2^k begins with exactly n consecutive increasing digits. 3
1, 7, 90, 155, 8290, 63293, 4338436, 5194868, 62759188 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The leading digit of the resulting powers of 2 are: 2, 1, 1, 4, 3, 1, 2, 1, 1. - Michel Marcus, Jul 11 2014

LINKS

Table of n, a(n) for n=1..9.

EXAMPLE

2^7 = 128 begins with 2 consecutive increasing digits ('12'). Thus a(2) = 7.

PROG

(Python)

def a(n):

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

....st = str(2**k)

....count = 0

....if len(st) > n:

......for i in range(len(st)):

........if int(st[i]) == int(st[i+1])-1:

..........count += 1

........else:

..........break

......if count == n:

........return k

n = 0

while n < 10:

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

..n += 1

CROSSREFS

Cf. A244848, A244851, A244852.

Sequence in context: A142995 A200832 A103064 * A321164 A243699 A007820

Adjacent sequences:  A244846 A244847 A244848 * A244850 A244851 A244852

KEYWORD

nonn,base,fini,full

AUTHOR

Derek Orr, Jul 07 2014

EXTENSIONS

a(7)-a(9) from Hiroaki Yamanouchi, Jul 10 2014

STATUS

approved

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Last modified October 14 14:06 EDT 2019. Contains 328017 sequences. (Running on oeis4.)