1,3

In sumset notation, number of subsets A of {1,...,n} such that the intersection of A and 2A is nonempty.

Table of n, a(n) for n=1..30.

Eric Weisstein's World of Mathematics, Sum-Free Set

a(n) = 2^n - A007865(n)

Cf. A007865 (number of sum-free subsets of 1..n).

Sequence in context: A293378 A041887 A129441 * A065497 A131727 A320236

Adjacent sequences: A093968 A093969 A093970 * A093972 A093973 A093974

nonn

T. D. Noe, Apr 20 2004

approved