|
Search: id:A055998
|
|
| |
|
| 0, 3, 7, 12, 18, 25, 33, 42, 52, 63, 75, 88, 102, 117, 133, 150, 168, 187, 207, 228, 250, 273, 297, 322, 348, 375, 403, 432, 462, 493, 525, 558, 592, 627, 663, 700, 738, 777, 817, 858, 900, 943, 987, 1032, 1078, 1125, 1173, 1222, 1272
(list; graph; listen)
|
|
|
OFFSET
|
0,2
|
|
|
COMMENT
|
a(n) = A126890(n,2) for n>1. - Reinhard Zumkeller (reinhard.zumkeller(AT)lhsystems.com), Dec 30 2006
If X is an n-set and Y a fixed (n-3)-subset of X then a(n-3) is equal to the number of 2-subsets of X intersecting Y. - Milan R. Janjic (agnus(AT)blic.net), Aug 15 2007
|
|
REFERENCES
|
A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, p. 193.
|
|
LINKS
|
Milan Janjic, Two Enumerative Functions
|
|
FORMULA
|
G.f.: x(3-2x)/(1-x)^3.
a(n)=C(n,2)-2*n ,n>=5 - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 25 2006
|
|
MAPLE
|
a:=n->sum(floor(k+2*n/(k+n)), k=2..n): seq(a(n), n=1..49); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Oct 01 2006
[seq(binomial(n, 2)-2*n , n=5..53)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Nov 25 2006
seq(sum(k-1 , k=4..n), n=3..51); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 28 2008
|
|
MATHEMATICA
|
Table[Sum[Binomial[k+1, k], {k, 2, n}], {n, 1, 49}] - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Mar 31 2007
|
|
CROSSREFS
|
Essentially the same as A027379. Equals A000217(n) - 3. Cf. A000096.
a(n) = A095660(n+1, 2): third column of (1, 3)-Pascal triangle.
Cf. A000096, A001477.
Adjacent sequences: A055995 A055996 A055997 this_sequence A055999 A056000 A056001
Sequence in context: A072098 A095115 A027379 this_sequence A066379 A024517 A005228
|
|
KEYWORD
|
easy,nonn
|
|
AUTHOR
|
Barry E. Williams, Jun 14 2000
|
|
|
Search completed in 0.002 seconds
|
