

A281663


Refactorable numbers that are not the sum of two refactorable numbers.


1




OFFSET

1,2


COMMENTS

Is this sequence finite?


LINKS

Table of n, a(n) for n=1..7.
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(nk)) == 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



