0,2

Sum of product of unordered pairs of numbers from {1..n+1}.

Number of edges of a complete k-partite graph of order k*(k+1)/2 (A000217), K_1,2,3,...,k. - Roberto E. Martinez II (remartin(AT)fas.harvard.edu), Oct 18 2001

This sequence holds the x^(n-2) coefficient of the characteristic polynomial of the N X N matrix A formed by MAX(i,j), where i is the row index and j is the column index of element A[i][j], 1 <= i,j <= N. Here N >= 2. - Paul M. Payton (paul.payton(AT)lmco.com), Sep 06 2005

S. Plouffe, Approximations de S\'{e}ries G\'{e}n\'{e}ratrices et Quelques Conjectures}, Dissertation, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 833.

G. E. Andrews, Number Theory, 1971, Dover Publications New York, p 4.

L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 227, #16.

F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 226.

H. S. Hall, S. R. Knight, Higher Algebra, Fourth Edition, Macmillan, 1891, p. 518.

T. D. Noe, Table of n, a(n) for n=0..1000

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, December 1972 [alternative scanned copy].

S. Plouffe, Approximations de S\'{e}ries G\'{e}n\'{e}ratrices et Quelques Conjectures}, Dissertation, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.

S. Plouffe, 1031 Generating Functions and Conjectures, Universit\'{e} du Qu\'{e}bec \`{a} Montr\'{e}al, 1992.

a(n)=binomial(n+2, 3)*(3*n+5)/4 = (n+1)*n*(n+2)*(3*n+5)/24. E.g.f.: exp(x)*x*(48+84*x+32*x^2+3*x^3)/24. G.f.: (2*x+x^2)/(1-x)^5.

a(n)=sum(i=1, n, i*(i+1)^2/2) - Jon Perry (perry(AT)globalnet.co.uk), Jul 31 2003

Examples include, E(K_1,2,3)=s(2+2,2)=11 and E(K_1,2,3,4,5)=s(4+2,4)=85, where E is the function that counts edges of graphs.

f:= n -> 1/24*(n+1)*n*(n+2)*(3*n+5);

A000914:=-(2+z)/(z-1)**5; [Conjectured by S. Plouffe in his 1992 dissertation.]

a:=n->sum((n-j)^3-(n-j)^2, j=1..n): seq(a(n)/2, n=2..39); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), May 26 2008

(PARI) a(n)=sum(i=1, n+1, sum(j=1, n+1, i*j*(i<j)))

Cf. A000217, A000290, A033428, A033581, A033583, A008275.

Sequence in context: A027229 A026946 A041389 this_sequence A086735 A078982 A078993

Adjacent sequences: A000911 A000912 A000913 this_sequence A000915 A000916 A000917

nonn,easy,nice

njas

More terms from Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 17 2000. Comments from Michael Somos, Jan 29, 2000.