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!)
 A257107 Composite numbers n such that n'=(n+12)', where n' is the arithmetic derivative of n. 0
 16, 65, 88, 209, 11009, 38009, 680609, 2205209, 2860198, 3515609, 4347209, 5365387, 5809361, 10595009, 12006209, 31979009, 83255059, 89019209, 152915402, 169130009, 172147423, 225869899, 244766009, 247590209, 258084209, 325622009, 357777209, 377330609 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS If the limitation of being composite is removed we also have the numbers p such that if p is prime then p + 12 is prime too (A046133). LINKS EXAMPLE 16' = (16 + 12)' = 28' = 32; 65' = (65 + 12)' = 77' = 18. MAPLE with(numtheory); P:= proc(q, h) local a, b, n, p; for n from 1 to q do if not isprime(n) then a:=n*add(op(2, p)/op(1, p), p=ifactors(n)[2]); b:=(n+h)*add(op(2, p)/op(1, p), p=ifactors(n+h)[2]); if a=b then print(n); fi; fi; od; end: P(10^9, 12); MATHEMATICA a[n_] := If[Abs@ n < 2, 0, n Total[#2/#1 & @@@ FactorInteger[Abs@ n]]]; Select[Range@ 100000, And[CompositeQ@ #, a@# == a[# + 12]] &] (* Michael De Vlieger, Apr 22 2015, after Michael Somos at A003415 *) CROSSREFS Cf. A003415, A046133, A226779. Sequence in context: A031446 A294584 A041492 * A249689 A043402 A044154 Adjacent sequences:  A257104 A257105 A257106 * A257108 A257109 A257110 KEYWORD nonn AUTHOR Paolo P. Lava, Apr 17 2015 EXTENSIONS a(16)-a(28) from Lars Blomberg, May 06 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 September 29 20:22 EDT 2020. Contains 337432 sequences. (Running on oeis4.)