OFFSET
1,1
COMMENTS
Invented by the HR mathematical theory formation program.
REFERENCES
S. Colton, Unpublished PhD Thesis, University of Edinburgh, 2000
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
Simon Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.
Simon Colton, HR - Automatic Theory Formation in Pure Mathematics
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 *)
PROG
(Magma) [k:k in [2..500 by 2]| IsIntegral(k/d) and IsEven(d) where d is #Divisors(k)]; // Marius A. Burtea, Jan 13 2020
CROSSREFS
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