The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A281663 Refactorable numbers that are not the sum of two refactorable numbers. 1
 1, 8, 12, 40, 56, 225, 441 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Is this sequence finite? LINKS S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999. Joshua Zelinsky, Tau Numbers: A Partial Proof of a Conjecture and Other Results , Journal of Integer Sequences, Vol. 5 (2002), Article 02.2.8 EXAMPLE 40 is a term because 40 is a refactorable number and there is no partition of 40 into two refactorable parts. PROG (PARI) isrefac(n) = (n%numdiv(n))==0; isok(n) = isrefac(n) && (sum(k=1, n\2, isrefac(k) && isrefac(n-k)) == 0); \\ Michel Marcus, Jan 26 2017 CROSSREFS Cf. A033950, A172398, A280634. Sequence in context: A024604 A025103 A307652 * A092179 A269726 A032410 Adjacent sequences: A281660 A281661 A281662 * A281664 A281665 A281666 KEYWORD nonn,more AUTHOR Altug Alkan, Jan 26 2017 STATUS approved

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

Last modified February 4 22:05 EST 2023. Contains 360082 sequences. (Running on oeis4.)