The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

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