A080573 Number of ways writing n as a sum of two distinct Ulam numbers.

0, 0, 1, 1, 2, 1, 2, 1, 2, 2, 1, 2, 1, 3, 2, 1, 3, 1, 4, 2, 2, 2, 0, 3, 0, 1, 2, 1, 4, 2, 2, 2, 0, 3, 0, 1, 2, 1, 4, 2, 2, 3, 0, 4, 0, 2, 1, 1, 4, 2, 3, 2, 1, 5, 2, 3, 1, 2, 3, 2, 3, 1, 3, 5, 3, 4, 0, 2, 1, 3, 2, 1, 5, 3, 5, 2, 1, 3, 2, 4, 2, 1, 5, 2, 6, 2, 1, 5, 2, 5, 2, 0, 4, 0, 6, 0

Offset: 1

Author

Naohiro Nomoto, Feb 22 2003

Keywords

• easy
• nonn

Comments

After about 10^5 terms, the plot of this sequences begins to show some structure. - T. D. Noe, Jan 21 2008

When a(n)=1, n is an Ulam number, A002858. A033629 has the terms when a(n)=0. - Jud McCranie, Jul 22 2012

Links

• T. D. Noe, Table of n, a(n) for n=1..10000
• T. D. Noe, Plot of 10^5 terms of A080573
• Rémy Sigrist, Density plot of the first million terms
• Rémy Sigrist, C program for A080573

Crossrefs

Cf. A002858, A033629.

Programs

C

See Links section.