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

1,5

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

Prog

(C) See Links section.

Crossrefs

Cf. A002858, A033629.

Sequence in context: A245920 A165413 A172155 * A186440 A006340 A270641

Adjacent sequences: A080570 A080571 A080572 * A080574 A080575 A080576

Keyword

easy,nonn

Author

Naohiro Nomoto, Feb 22 2003

Status

approved