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 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(13) > 1116000. - Chai Wah Wu, Dec 17 2014 a(14) > 7*10^6. - Giovanni Resta, Apr 20 2016 LINKS Table of n, a(n) for n=1..15. 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 # Derek Orr, Jul 28 2014 (Python) def A215730(n): ....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' # Chai Wah Wu, Dec 17 2014 CROSSREFS Cf. A215736, A045875. Sequence in context: A254502 A025524 A042841 * A187508 A087725 A273790 Adjacent sequences: A215727 A215728 A215729 * A215731 A215732 A215733 KEYWORD nonn,base,hard AUTHOR V. Raman, Aug 22 2012 EXTENSIONS Added a(10), Rick van der Hoorn, Mar 26 2013 a(11)-a(12) from Hiroaki Yamanouchi, Aug 29 2014 a(13) from Giovanni Resta, Apr 19 2016 a(14)-a(15) from Bert Dobbelaere, Feb 15 2019 STATUS approved

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Last modified December 8 14:49 EST 2023. Contains 367680 sequences. (Running on oeis4.)