

A215730


a(n) is the smallest m for which 7^m contains n consecutive identical digits.


14



0, 6, 31, 71, 172, 175, 1961, 6176, 33836, 61282, 305871, 856635, 2135396, 7291510, 11032874
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OFFSET

1,2


COMMENTS



LINKS



EXAMPLE

7^31 = 157775382034845806615042743 contains 3 consecutive identical digits.


PROG

(Python)
def a(n):
..st = "0123456789"
..for k in range(10**6):
....s = str(7**k)
....tot = 0
....for i in st:
......if s.count(i*n) > 0:
........tot += 1
........break
....if tot > 0:
......return k
n = 1
while n < 10:
..print(a(n), end=', ')
..n += 1
(Python)
....l, x = [str(d)*n for d in range(10)], 1
....for m in range(10**9):
........s = str(x)
........for k in l:
............if k in s:
................return m
........x *= 7
....return 'search limit reached'


CROSSREFS



KEYWORD

nonn,base,hard


AUTHOR



EXTENSIONS



STATUS

approved



