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 A057265 Even refactorable numbers (i.e., the number of divisors is itself a divisor and it is also even). 11
 2, 8, 12, 18, 24, 40, 56, 60, 72, 80, 84, 88, 96, 104, 108, 128, 132, 136, 152, 156, 180, 184, 204, 228, 232, 240, 248, 252, 276, 288, 296, 328, 344, 348, 360, 372, 376, 384, 396, 424, 444, 448, 450, 468, 472, 480, 488, 492 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Invented by the HR mathematical theory formation program. REFERENCES S. Colton, Unpublished PhD Thesis, University of Edinburgh, 2000 LINKS S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2. EXAMPLE 18 is refactorable because tau(18) = 6 and 6 divides 18 and 18 is even. MATHEMATICA rfnQ[n_]:=Module[{ds=DivisorSigma[0, n]}, Divisible[n, ds] && EvenQ[ds]]; Select[Range[2, 500, 2], rfnQ]  (* Harvey P. Dale, Mar 14 2011 *) CROSSREFS Cf. A033950, A036896. Sequence in context: A090772 A046525 A235353 * A099418 A108987 A035405 Adjacent sequences:  A057262 A057263 A057264 * A057266 A057267 A057268 KEYWORD easy,nonn AUTHOR Simon Colton (simonco(AT)cs.york.ac.uk), Aug 21 2000 EXTENSIONS Corrected (erroneous term 36 removed) by Harvey P. Dale, Mar 14 2011 STATUS approved

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Last modified June 24 14:30 EDT 2019. Contains 324325 sequences. (Running on oeis4.)