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A014844 a(n) = 2^n - n*(n-1)/2. 3
1, 2, 3, 5, 10, 22, 49, 107, 228, 476, 979, 1993, 4030, 8114, 16293, 32663, 65416, 130936, 261991, 524117, 1048386, 2096942, 4194073, 8388355, 16776940, 33554132, 67108539, 134217377, 268435078, 536870506, 1073741389, 2147483183 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(n) is the number of subsets of {1,2,...,n} that do not have a cardinality of 2. - Geoffrey Critzer, Feb 25 2012

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

FORMULA

E.g.f.: exp(x)*(exp(x)-x^2/2!). - Geoffrey Critzer, Feb 25 2012

G.f.: (1-3*x+2*x^2+x^3)/((1-x)^3*(1-2*x)). - Colin Barker, Apr 01 2012

MATHEMATICA

nn = 20; Range[0, nn]! CoefficientList[Series[Exp[x] (Exp[x] - x^2/2!), {x, 0, nn}], x] (* Geoffrey Critzer, Feb 25 2012 *)

CoefficientList[Series[(1-3*x+2*x^2+x^3)/((1-x)^3*(1-2*x)), {x, 0, 33}], x] (* Vincenzo Librandi, Apr 18 2012 *)

PROG

(MAGMA) [2^n - n*(n-1)/2: n in [0..40]]; // Vincenzo Librandi, Apr 18 2012

CROSSREFS

Sequence in context: A001646 A103595 A293842 * A307264 A329244 A173271

Adjacent sequences:  A014841 A014842 A014843 * A014845 A014846 A014847

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified June 5 03:12 EDT 2020. Contains 334828 sequences. (Running on oeis4.)