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a(n) is the smallest m for which 5^m contains n consecutive identical digits.
14

%I #26 Apr 18 2020 08:05:06

%S 0,11,50,95,125,1087,2786,2790,2796,2797,2802,2803,1040703,5547565,

%T 7761841,17876345

%N a(n) is the smallest m for which 5^m contains n consecutive identical digits.

%C a(13) > 893000. - _Chai Wah Wu_, Dec 17 2014

%o (Python)

%o def A215728(n):

%o l, x = [str(d)*n for d in range(10)], 1

%o for m in range(10**9):

%o s = str(x)

%o for k in l:

%o if k in s:

%o return m

%o x *= 5

%o return 'search limit reached'

%o # _Chai Wah Wu_, Dec 17 2014

%Y Cf. A215734, A045875.

%K nonn,base,more

%O 1,2

%A _V. Raman_, Aug 22 2012

%E a(13)-a(14) from _Giovanni Resta_, Apr 19 2016

%E a(15)-a(16) from _Bert Dobbelaere_, Feb 13 2019