cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-2 of 2 results.

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

Original entry on oeis.org

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

Views

Author

Altug Alkan, Jan 26 2017

Keywords

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

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

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

Original entry on oeis.org

2, 9, 18, 24, 60, 88, 625, 1089, 2601, 1500625
Offset: 1

Views

Author

Altug Alkan, Feb 17 2017

Keywords

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.

Examples

			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.

Links

Crossrefs

Cf. A033950, A172398, A280634, A281663.

Extensions

a(10) from Giovanni Resta, Feb 17 2017
Showing 1-2 of 2 results.

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