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A030000 a(n) = smallest nonnegative number k such that the decimal expansion of 2^k contains the string n. 21
10, 0, 1, 5, 2, 8, 4, 15, 3, 12, 10, 40, 7, 17, 18, 21, 4, 27, 30, 13, 11, 18, 43, 41, 10, 8, 18, 15, 7, 32, 22, 17, 5, 25, 27, 25, 16, 30, 14, 42, 12, 22, 19, 22, 18, 28, 42, 31, 11, 32, 52, 9, 19, 16, 25, 16, 8, 20, 33, 33, 23, 58, 18, 14, 6, 16, 46, 24, 15, 34, 29, 21, 17, 30 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Giovanni Resta, Table of n, a(n) for n = 0..10000 (terms up to a(1000) from T. D. Noe)

EXAMPLE

2^12 = 4096 is first power of 2 containing a 9, so a(9) = 12.

MATHEMATICA

Table[ i=0; While[ StringPosition[ ToString[ 2^i ], ToString[ n ] ]=={}, i++ ]; i, {n, 0, 80} ]

PROG

(Haskell)

import Data.List (isInfixOf, findIndex)

import Data.Maybe (fromJust)

a030000 n =

   fromJust $ findIndex (show n `isInfixOf`) $ map show a000079_list

-- Reinhard Zumkeller, Aug 04 2011

CROSSREFS

Cf. A030001 (the actual powers of 2), A063565, A018856, A000079.

See also A321043.

Sequence in context: A288123 A261334 A038689 * A221809 A291451 A323836

Adjacent sequences:  A029997 A029998 A029999 * A030001 A030002 A030003

KEYWORD

nonn,base

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from Hans Havermann

STATUS

approved

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Last modified November 21 04:22 EST 2019. Contains 329350 sequences. (Running on oeis4.)