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

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

Offset: 1

Author

Altug Alkan, Jan 26 2017

Keywords

• nonn
• more

Comments

Is this sequence finite?

Examples

			40 is a term because 40 is a refactorable number and there is no partition of 40 into two refactorable parts.
		

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

Crossrefs

Cf. A033950, A172398, A280634.

Programs

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