A226429 Number of numerical semigroups S of genus 3^n having a minimal generating set of cardinality 2.

2, 3, 4, 4, 5, 7, 8, 9, 8, 9, 11, 13, 11, 15, 16, 14, 14, 18, 20, 21

Offset: 1

Author

Arkadiusz Wesolowski, Jun 06 2013

Keywords

• nonn
• more

Links

• Shalom Eliahou and Jorge Ramírez Alfonsín, Two-generator numerical semigroups and Fermat and Mersenne numbers, SIAM J. Discrete Math., 25(2), 2011, 622-630.

Crossrefs

Cf. A003307, A079363.

Formula

a(n) = n + 1 if 2*3^n - 1 is prime.

a(n) ~ n + 1.