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A226219 Least k > 1 not a power of 10 such that n is a substring of k*n. 1
2, 11, 6, 11, 6, 3, 6, 11, 6, 11, 11, 101, 26, 87, 51, 21, 26, 69, 51, 63, 6, 58, 51, 97, 26, 5, 51, 101, 26, 79, 11, 101, 26, 101, 51, 21, 26, 101, 51, 87, 6, 59, 34, 101, 26, 21, 51, 74, 26, 51, 3, 69, 26, 29, 51, 21, 26, 101, 51, 27, 6, 92, 51, 26, 26, 21 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Paul Tek, Table of n, a(n) for n = 0..10000

FORMULA

a(n) <= 10^A055642(n)+1.

MATHEMATICA

Table[k = 2; While[IntegerQ[Log[10, k]] || StringPosition[ToString[k*n], ToString[n], 1] == {}, k++]; k, {n, 0, 100}] (* T. D. Noe, May 31 2013 *)

PROG

(Perl) sub a {

    my $n = shift;

    my $k = 2;

    while (1) {

        if ($k !~ /^10+$/) {

            if (index($k*$n, $n)>=0) {

                return $k;

            }

        }

        $k++;

    }

}

(Haskell)

import Data.List (isInfixOf, isPrefixOf)

a226219 n = head [k | k <- [2..],

                      isInfixOf (show n) (show (k*n)), not $ p10 k]

   where p10 = flip isPrefixOf ('1' : repeat '0') . show  :: Int -> Bool

-- Reinhard Zumkeller, May 31 2013

CROSSREFS

Cf. A045537.

Sequence in context: A158616 A127821 A114724 * A285866 A165768 A323783

Adjacent sequences:  A226216 A226217 A226218 * A226220 A226221 A226222

KEYWORD

base,nonn

AUTHOR

Paul Tek, May 31 2013

STATUS

approved

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Last modified July 25 08:42 EDT 2021. Contains 346285 sequences. (Running on oeis4.)