A226429 - OEIS

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A226429

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

0

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

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OFFSET

1,1

LINKS

Table of n, a(n) for n=1..20.

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

FORMULA

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

a(n) ~ n + 1.

CROSSREFS

Cf. A003307, A079363.

Sequence in context: A036416 A084618 A075518 * A036820 A017829 A017843

Adjacent sequences: A226426 A226427 A226428 * A226430 A226431 A226432

KEYWORD

nonn,more

AUTHOR

Arkadiusz Wesolowski, Jun 06 2013

STATUS

approved