A258738 Numbers m such that the concatenation of k and the k-th divisor of m is equal to m for some k.

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

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 A366093

Adjacent sequences: A258735 A258736 A258737 * A258739 A258740 A258741

Keyword

nonn,base

Author

Michel Marcus, Jun 08 2015

Status

approved