A281663 Refactorable numbers that are not the sum of two refactorable numbers.

1, 8, 12, 40, 56, 225, 441

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