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A003240 Number of partially achiral rooted trees.
(Formerly M1123)
1
1, 1, 2, 4, 8, 16, 31, 62, 120, 236, 454, 884, 1697, 3275, 6266, 12020, 22935, 43788, 83325, 158516, 300914, 570794, 1081157, 2045934, 3867617, 7304149, 13783221, 25984936, 48956715, 92155376, 173376484, 325919786, 612378787, 1149777034 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

REFERENCES

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

LINKS

Herman Jamke (hermanjamke(AT)fastmail.fm), Feb 26 2008, Table of n, a(n) for n = 1..70

F. Harary and R. W. Robinson, The number of achiral trees, J. Reine Angew. Math., 278 (1975), 322-335.

F. Harary and R. W. Robinson, The number of achiral trees, J. Reine Angew. Math., 278 (1975), 322-335. (Annotated scanned copy)

Index entries for sequences related to rooted trees

Index entries for sequences related to trees

PROG

(PARI) t(n)=local(A=x); if(n<1, 0, for(k=1, n-1, A/=(1-x^k+x*O(x^n))^polcoeff(A, k)); polcoeff(A, n)) {n=100; Ty2=sum(i=0, 100, t(i)*y^(2*i)); p=subst(y*Ty2/(y-Ty2), y, y+y*O(y^n)); p=Pol(p, y); r=subst(Ty2*(y+p+(p^2-subst(p, y, y^2))/(2*y))/y^2, y, x+x*O(x^n)); for(i=0, n-2, print1(polcoeff(r, i)", "))} - Herman Jamke (hermanjamke(AT)fastmail.fm), Feb 26 2008

CROSSREFS

Sequence in context: A239557 A001591 A194628 * A280543 A282566 A251706

Adjacent sequences:  A003237 A003238 A003239 * A003241 A003242 A003243

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Feb 26 2008

STATUS

approved

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Last modified January 20 23:17 EST 2019. Contains 319336 sequences. (Running on oeis4.)