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A121319 a(n) is the smallest number k such that k and 2^k have the same last n digits. Here k must have at least n digits (cf. A113627). 4
14, 36, 736, 8736, 48736, 948736, 2948736, 32948736, 432948736, 3432948736, 53432948736, 353432948736, 5353432948736, 75353432948736, 1075353432948736, 5075353432948736, 15075353432948736, 615075353432948736, 8615075353432948736, 98615075353432948736 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Jon E. Schoenfield, Table of n, a(n) for n = 1..80

Jon E. Schoenfield, Excel program

FORMULA

If A109405(n) has n digits, a(n) = A109405(n), otherwise a(n) = A109405(n) + 10^n. - Max Alekseyev, May 05 2007

EXAMPLE

2^14 = 16384 and 14 end with the same single digit 4, thus a(1) = 14.

MATHEMATICA

f[n_] := Block[{k = If[n == 1, 2, 10], m = 10^n}, While[ PowerMod[2, k, m] != Mod[k, m], k += 2]; k]; Do[ Print@f@n, {n, 9}] (* Robert G. Wilson v *)

PROG

(PARI) A121319(n) = { local(k, tn); tn=10^n ; forstep(k=2, 1000000000, 2, if ( k % tn == (2^k) % tn, return(k) ; ) ; ) ; return(0) ; } { for(n = 1, 13, print( A121319(n)) ; ) ; } \\ R. J. Mathar, Aug 27 2006

CROSSREFS

Cf. A007185, A016090, A003226, A035383, A064540, A064541, A109405.

Sequence in context: A279900 A263125 A113627 * A034181 A216766 A057439

Adjacent sequences:  A121316 A121317 A121318 * A121320 A121321 A121322

KEYWORD

nonn,base

AUTHOR

Tanya Khovanova, Aug 25 2006

EXTENSIONS

a(6)-a(9) from Robert G. Wilson v and Jon E. Schoenfield, Aug 26 2006

a(10) from Robert G. Wilson v, Sep 26 2006

a(11)-a(16) from Alexander Adamchuk, Jan 28 2007

a(16) corrected by Max Alekseyev, Apr 12 2007

STATUS

approved

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Last modified September 24 20:09 EDT 2018. Contains 315356 sequences. (Running on oeis4.)