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A067969 Number of nodes in virtual, "optimal", chordal graphs of diameter 5, degree =n+1. 1
11, 20, 61, 102, 231, 360, 681, 1002, 1683, 2364, 3653, 4942, 7183, 9424, 13073, 16722, 22363, 28004, 36365, 44726, 56695, 68664, 85305, 101946, 124515, 147084, 177045, 207006, 246047, 285088, 335137, 385186, 448427, 511668, 590557, 669446 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

Concrete Mathematics - R. L. Graham, D. E. Knuth, O. Patashnik, 1994,Addison-Wesley Company, Inc.

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

FORMULA

n - odd: t=(n+1)/2, a[n] := 4/15*t^5+2/3*t^4+8/3*t^3+10/3*t^2+46/15*t+1; n - even: t=n/2, a(n) := (4/15*t^5+2/3*t^4+8/3*t^3+10/3*t^2+46/15*t+1)+((2*(t*(t+1)*(t^2+t+4))/3)+1)

G.f.: x*(11-2*x-12*x^2+8*x^3+26*x^4-12*x^5-12*x^6+8*x^7+3*x^8-2*x^9)/ ((1+x)^4 * (x-1)^6) [From Maksym Voznyy (voznyy(AT)mail.ru), Jul 28 2009]

EXAMPLE

a(5)=231 n=odd, t=3, a(5)=324/5+54+72+30+46/5+1=231 a(6)=360 n=even, t=3, a(6)=231+(24*16)/3+1=231+128+1=360

MAPLE

for n from 1 to k do if ((n mod 2 ) = 1) then t := (n+1)/2; a[n] := 4/15*t^5+2/3*t^4+8/3*t^3+10/3*t^2+46/15*t+1; else t := n/2; a[n] := ((4/15*t^5+2/3*t^4+8/3*t^3+10/3*t^2+46/15*t+1)+((2*(t*(t+1)*(t^2+t+4))/3)+1)); fi; print(a[n]); od;

CROSSREFS

Cf. A001847.

Sequence in context: A164576 A058497 A134782 * A068599 A180113 A198310

Adjacent sequences:  A067966 A067967 A067968 * A067970 A067971 A067972

KEYWORD

nonn

AUTHOR

S. Bujnowski & B. Dubalski (slawb(AT)atr.bydgoszcz.pl), Mar 11 2002

EXTENSIONS

G.f. proposed by Maksym Voznyy checked and corrected by R. J. Mathar, Sep 16 2009.

STATUS

approved

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Last modified July 4 14:51 EDT 2020. Contains 335448 sequences. (Running on oeis4.)