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A014236 G.f.: 2*x*(1-x)/((1-2*x)(1-2*x^2)). 2
0, 2, 2, 8, 12, 32, 56, 128, 240, 512, 992, 2048, 4032, 8192, 16256, 32768, 65280, 131072, 261632, 524288, 1047552, 2097152, 4192256, 8388608, 16773120, 33554432, 67100672, 134217728, 268419072 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Number of symmetric chiral (optically active) isomers possible for organic compounds with n distinct carbon atoms.

A020522 interleaved with A004171 and apparently the number of asymmetric Dyck (n+2)-paths with exactly half of the steps lying between the first and last peaks; e.g. all asymmetric 3-paths (UU*DDU*D and U*DUU*DD) comply so a(1)=2. - David Scambler, Sep 14 2012

LINKS

Table of n, a(n) for n=0..28.

Index entries for linear recurrences with constant coefficients, signature (2,2,-4).

FORMULA

a(n) = 2*A007179(n). - R. J. Mathar, Nov 14 2011

MAPLE

f := n -> if n mod 2 = 0 then 2^n-2^(n/2) else 2^n; fi;

CROSSREFS

Second differences of A027556.

Sequence in context: A053414 A189837 A274409 * A087955 A026537 A089248

Adjacent sequences:  A014233 A014234 A014235 * A014237 A014238 A014239

KEYWORD

nonn,easy

AUTHOR

Paul F. Hudrlik (hudrlik(AT)scs.howard.edu)

EXTENSIONS

G.f. corrected by Olivier GĂ©rard, Nov 13 2011

STATUS

approved

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Last modified September 22 09:43 EDT 2017. Contains 292337 sequences.