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A094374 a(n)=(3^n-1)/2+2^n. 3
1, 3, 8, 21, 56, 153, 428, 1221, 3536, 10353, 30548, 90621, 269816, 805353, 2407868, 7207221, 21588896, 64701153, 193972388, 581655021, 1744440776, 5232273753, 15694724108, 47079978021, 141231545456, 423677859153, 1271000023028 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Binomial transform of A094373.

Row sums of A125103. - Paul Barry, Dec 04 2007

Let P(A) be the power set of an n-element set A. Then a(n) = the number of pairs of elements {x,y} of P(A) for which either 0) x and y are disjoint and for which either x is a subset of y or y is a subset of x, or 1) x and y are disjoint and for which x is not a subset of y and y is not a subset of x, or 2) x = y. - Ross La Haye, Jan 11 2008

REFERENCES

Ross La Haye, Binary Relations on the Power Set of an n-Element Set, Journal of Integer Sequences, Vol. 12 (2009), Article 09.2.6

LINKS

Table of n, a(n) for n=0..26.

Index to sequences with linear recurrences with constant coefficients, signature (6,-11,6).

FORMULA

G.f.: (1-3x+x^2)/((1-x)(1-2x)(1-3x)); a(n)=6a(n-1)-11a(n-2)+6a(n-3). a(n)=A003462(n)+A000079(n).

a(n)=sum{k=0..n, C(n,k)+2^k*C(n,k+1)}; - Paul Barry, Dec 04 2007

a(n) = StirlingS2(n+1,3) + 2*StirlingS2(n+1,2) + 1. - Ross La Haye, Jan 11 2008

a(0)=1, a(1)=3, a(2)=8, a(n)=6*a(n-1)-11*a(n-2)+6*a(n-3). - Harvey P. Dale, Jul 22 2013

MATHEMATICA

Table[(3^n-1)/2+2^n, {n, 0, 30}] (* or *) LinearRecurrence[{6, -11, 6}, {1, 3, 8}, 30] (* Harvey P. Dale, Jul 22 2013 *)

CROSSREFS

Cf. A000225, A000392, A000079.

Sequence in context: A090413 A128105 A085560 * A008909 A006835 A014318

Adjacent sequences:  A094371 A094372 A094373 * A094375 A094376 A094377

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Apr 28 2004

STATUS

approved

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Last modified April 19 21:10 EDT 2014. Contains 240777 sequences.