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A131536
Exponent of least power of 2 having exactly n consecutive 2's in its decimal representation.
9
0, 1, 51, 43, 692, 314, 2354, 8555, 13326, 81784, 279272, 865356, 1727608, 1727602, 23157022, 63416790
OFFSET
0,3
LINKS
Popular Computing (Calabasas, CA), Two Tables, Vol. 1, (No. 9, Dec 1973), page PC9-16.
EXAMPLE
a(3)=43 because 2^43(i.e. 8796093022208) is the smallest power of 2 to contain a run of 3 consecutive twos in its decimal form.
MATHEMATICA
a = ""; Do[ a = StringJoin[a, "2"]; b = StringJoin[a, "2"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
PROG
(Python)
def A131536(n):
s, t, m, k, u = '2'*n, '2'*(n+1), 0, 1, '1'
while s not in u or t in u:
m += 1
k *= 2
u = str(k)
return m # Chai Wah Wu, Jan 28 2020
CROSSREFS
KEYWORD
more,nonn,base
AUTHOR
Shyam Sunder Gupta, Aug 26 2007
EXTENSIONS
3 more terms from Sean A. Irvine, Jul 19 2010
a(14) from Lars Blomberg, Jan 24 2013
a(15) from Bert Dobbelaere, Feb 25 2019
a(0) from Chai Wah Wu, Jan 28 2020
STATUS
approved