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A037852 Number of normal subgroups of dihedral group with 2n elements. 1
2, 5, 3, 6, 3, 7, 3, 7, 4, 7, 3, 9, 3, 7, 5, 8, 3, 9, 3, 9, 5, 7, 3, 11, 4, 7, 5, 9, 3, 11, 3, 9, 5, 7, 5, 12, 3, 7, 5, 11, 3, 11, 3, 9, 7, 7, 3, 13, 4, 9, 5, 9, 3, 11, 5, 11, 5, 7, 3, 15, 3, 7, 7, 10, 5, 11, 3, 9, 5, 11, 3, 15, 3, 7, 7 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

When n is an odd prime a(n) = 3.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..1001

FORMULA

a(n) = d(n) + 2 + (-1)^n. - Paul Boddington, Feb 02 2004

a(n) = A000005(n) + A176040(n). - Michel Marcus, Aug 19 2015

PROG

(PARI) a(n) = numdiv(n) + 2 + (-1)^n \\ Michel Marcus, Jul 30 2013

CROSSREFS

Cf. A062249, A007503, A062553.

Cf. A000005, A176040.

Sequence in context: A085825 A198140 A212614 * A226214 A160516 A264105

Adjacent sequences:  A037849 A037850 A037851 * A037853 A037854 A037855

KEYWORD

nonn

AUTHOR

Ahmed Fares (ahmedfares(AT)my-deja.com), Jul 04 2001

EXTENSIONS

More terms from Michel Marcus, Jul 30 2013

STATUS

approved

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Last modified October 21 11:25 EDT 2019. Contains 328295 sequences. (Running on oeis4.)