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A258738 Numbers m such that the concatenation of k and the k-th divisor of m is equal to m for some k. 1
11, 22, 25, 410, 425, 620, 735, 816, 832, 850, 975, 1280, 1872, 5125, 7175, 12500, 14200, 17200, 19250, 24150, 42336, 46920, 141250, 222500, 251250, 262000, 291450, 305000, 402500, 442750, 515100, 595000, 627750, 787500, 855000, 871200, 2015625, 2234375, 4213125 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Inspired by A257491.

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..70

EXAMPLE

The 1st divisor of 11 is 1, and the concatenation of 1 and 1 is 11.

The 2nd divisor of 25 is 5, and the concatenation of 2 and 5 is 25.

MATHEMATICA

Select[Range[10^5], (d = Divisors[n=#]; {} != Select[ Range@ Length@ d, FromDigits@ Flatten[ IntegerDigits /@{#, d[[#]]}] == n &, 1]) &] (* Giovanni Resta, Jun 08 2015 *)

PROG

(PARI) isok(n) = {d = divisors(n); for (k=1, #d, if (eval(concat(Str(k), Str(d[k]))) == n, return (1)); ); }

(Haskell)

a258738 n = a258738_list !! (n-1)

a258738_list = f [1..] where

   f (x:xs) = if show x `elem` zipWith (++) kss (map show $ a027750_row' x)

                 then x : f xs else f xs

   kss = map show [1..]

-- Reinhard Zumkeller, Jun 10 2015

CROSSREFS

Cf. A257491.

Cf. A027750.

Sequence in context: A332516 A066500 A234314 * A160272 A164006 A178736

Adjacent sequences:  A258735 A258736 A258737 * A258739 A258740 A258741

KEYWORD

nonn,base

AUTHOR

Michel Marcus, Jun 08 2015

STATUS

approved

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Last modified June 5 15:37 EDT 2020. Contains 334852 sequences. (Running on oeis4.)