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%I #12 Jun 10 2015 06:56:46
%S 11,22,25,410,425,620,735,816,832,850,975,1280,1872,5125,7175,12500,
%T 14200,17200,19250,24150,42336,46920,141250,222500,251250,262000,
%U 291450,305000,402500,442750,515100,595000,627750,787500,855000,871200,2015625,2234375,4213125
%N Numbers m such that the concatenation of k and the k-th divisor of m is equal to m for some k.
%C Inspired by A257491.
%H Reinhard Zumkeller, <a href="/A258738/b258738.txt">Table of n, a(n) for n = 1..70</a>
%e The 1st divisor of 11 is 1, and the concatenation of 1 and 1 is 11.
%e The 2nd divisor of 25 is 5, and the concatenation of 2 and 5 is 25.
%t Select[Range[10^5], (d = Divisors[n=#]; {} != Select[ Range@ Length@ d, FromDigits@ Flatten[ IntegerDigits /@{#, d[[#]]}] == n &, 1]) &] (* _Giovanni Resta_, Jun 08 2015 *)
%o (PARI) isok(n) = {d = divisors(n); for (k=1, #d, if (eval(concat(Str(k), Str(d[k]))) == n, return (1)););}
%o (Haskell)
%o a258738 n = a258738_list !! (n-1)
%o a258738_list = f [1..] where
%o f (x:xs) = if show x `elem` zipWith (++) kss (map show $ a027750_row' x)
%o then x : f xs else f xs
%o kss = map show [1..]
%o -- _Reinhard Zumkeller_, Jun 10 2015
%Y Cf. A257491.
%Y Cf. A027750.
%K nonn,base
%O 1,1
%A _Michel Marcus_, Jun 08 2015
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