0,3

G. Polya, Algebraische Berechnung der Anzahl der Isomeren einiger organischer Verbindungen, Zeit. f. Kristall., 93 (1936), 415-443.

N. J. A. Sloane, Table of n, a(n) for n = 0..100

Frederic Chyzak, Enumerating alcohols and other classes of chemical molecules

G.f.: A(x) = x*A000598(x)/(1-A000642(x))^3.

The following Maple commands are taken from the Chyzak web site:

with(combstruct);

gramm_Alkyl:=Alkyl=Prod(Carbon, Set(Alkyl, card<=3)), Carbon=Atom:

specs_Alkyl:=[Alkyl, {gramm_Alkyl}, unlabeled]:

gramm_S1_Alkyl:=S1_Alkyl[X]=Union(Prod(Carbon, S1_Alkyl[X], Set(Alkyl, card<=2)), Prod(Prod(Carbon, X), Set(Alkyl, card<=2))), X=Epsilon:

specs_S1_Alkyl:=[S1_Alkyl[X], {gramm_S1_Alkyl, gramm_Alkyl}, unlabeled]:

gramm_S2_Alkyl:=S2_Alkyl[X, Y]=Union(Prod(Carbon, S2_Alkyl[X, Y], Set(Alkyl, card<=2)), Prod(Carbon, Union(S1_Alkyl[X], X), Union(S1_Alkyl[Y], Y), Set(Alkyl, card<=1))):

specs_S2_Alkyl:=[S2_Alkyl[X, Y], {gramm_S2_Alkyl, gramm_S1_Alkyl, op(subs(X=Y, [gramm_S1_Alkyl])), gramm_Alkyl}, unlabeled]:

[seq(count(specs_S2_Alkyl, size=i), i=0..50)];

Adjacent sequences: A000637 A000638 A000639 this_sequence A000641 A000642 A000643

Sequence in context: A121654 A036366 A109454 this_sequence A010919 A022029 A010900

nonn,easy

njas