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A112951 Number of indecomposable Schur rings over the field Z_{2^n}. 0
1, 2, 5, 16, 63, 271, 1225, 5726, 27461, 134461, 669795, 3384945, 17316771, 89518347, 466932059, 2454546192, 12990743783, 69164599115, 370186756425, 1990638982239, 10749412063853, 58265968105385, 316903203993921 (list; graph; refs; listen; history; internal format)
OFFSET

1,2

COMMENTS

Counts also special lattice paths combining ones enumerated by the Catalan numbers A000108 and the large Schroeder numbers A006318.

LINKS

I. Kov\'acs, The number of indecomposable Schur rings over a cyclic 2-group,S\'eminaire Lotharingien de Combinatoire, vol. 51 (2005), Article B51h.

FORMULA

G.f.: 2/(3x+sqrt(1-4x)+sqrt(1-6x+x^2))+x/(1-x).

CROSSREFS

Cf. A000108, A006318.

Sequence in context: A159603 A058117 A007124 * A124470 A105072 A022494

Adjacent sequences:  A112948 A112949 A112950 * A112952 A112953 A112954

KEYWORD

nonn

AUTHOR

Valery A. Liskovets (liskov(AT)im.bas-net.by), Oct 10 2005

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Last modified February 17 21:13 EST 2012. Contains 206085 sequences.