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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

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(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

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Last modified February 21 23:00 EST 2020. Contains 332113 sequences. (Running on oeis4.)