A282519 Refactorable numbers that are the sum of two refactorable numbers in exactly one way.

2, 9, 18, 24, 60, 88, 625, 1089, 2601, 1500625

Offset

1,1

Comments

Sequence is a result of investigation on the marked region in graph of A172398(A033950(n)) that is in Links section. Also there are other sequences that marked region has.

Links

Table of n, a(n) for n=1..10.

Altug Alkan, Illustration of A172398(A033950(n))

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

Refactorable number 1500625 is a term because 1500625 is the sum of two refactorable numbers in exactly one way, that is, 1500625 = 5^4 * 7^4 = 3^2 * 131^2 + 2^7 * 13 * 809.

Crossrefs

Cf. A033950, A172398, A280634, A281663.

Sequence in context: A346102 A346233 A358946 * A359580 A103256 A028881

Adjacent sequences: A282516 A282517 A282518 * A282520 A282521 A282522

Keyword

nonn,more

Author

Altug Alkan, Feb 17 2017

Extensions

a(10) from Giovanni Resta, Feb 17 2017

Status

approved