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A281663
Refactorable numbers that are not the sum of two refactorable numbers.
1
1, 8, 12, 40, 56, 225, 441
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
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Jan 26 2017
STATUS
approved