A203422 -id:A203422 - cp's OEIS frontend

A203423 a(n) = w(n+1)/(2*w(n)), where w=A203422.

-3, 24, -250, 3240, -50421, 917504, -19131876, 450000000, -11789738455, 340545503232, -10752962364222, 368510430439424, -13623365478515625, 540431955284459520, -22899384412078526344, 1032236014321051140096, -49323481720063219673451, 2490368000000000000000000, -132484966403310261255807810

Offset: 1

Clark Kimberling, Jan 02 2012

sign

G. C. Greubel, Table of n, a(n) for n = 1..350

Cf. A000169, A053506, A203421, A203422.

[(-1)^n*(n+1)*(n+2)^n/2: n in [1..20]]; // G. C. Greubel, Dec 07 2023

(* First program *)
f[j_] := 1/(j + 1); z = 16;
v[n_] := Product[Product[f[k] - f[j], {j, 1, k - 1}], {k, 2, n}]
1/Table[v[n], {n, 1, z}]             (* A203422 *)
Table[v[n]/(2 v[n + 1]), {n, 1, z}]  (* this sequence *)
(* Second program *)
Table[(-1)^n*(n+1)*(n+2)^n/2, {n,20}] (* G. C. Greubel, Dec 07 2023 *)

[(-1)^n*(n+1)*(n+2)^n/2 for n in range(1,21)] # G. C. Greubel, Dec 07 2023

a(n) = (-1)^n*A053506(n+2)/2. - Steven Finch, Apr 16 2022

E.g.f.: -(1/(2*x^2))*( W(x)/(1 + W(x))^3 - 2*W(x)/(1 + W(x)) + W(x) + x^2), where W(x) = LambertW(x). - G. C. Greubel, Dec 07 2023

A093883 Product of all possible sums of two distinct numbers taken from among first n natural numbers.

Original entry on oeis.org

1, 3, 60, 12600, 38102400, 2112397056000, 2609908810629120000, 84645606509847871488000000, 82967862872337478796810649600000000, 2781259372192376861719959017613164544000000000

Offset: 1

Amarnath Murthy, Apr 22 2004

nonn

From Clark Kimberling, Jan 02 2013: (Start)
Each term divides its successor, as in A006963, and by the corresponding superfactorial, A000178(n), as in A203469.
Abbreviate "Vandermonde" as V. The V permanent of a set S={s(1),s(2),...,s(n)} is a product of sums s(j)+s(k) in analogy to the V determinant as a product of differences s(k)-s(j). Let D(n) and P(n) denote the V determinant and V permanent of S, and E(n) the V determinant of the numbers s(1)^2, s(2)^2, ..., s(n)^2; then P(n) = E(n)/D(n). This is one of many divisibility properties associated with V determinants and permanents. Another is that if S consists of distinct positive integers, then D(n) divides D(n+1) and P(n) divides P(n+1).
Guide to related sequences:
...
s(n).............. D(n)....... P(n)
n................. A000178.... (this)
n+1............... A000178.... A203470
n+2............... A000178.... A203472
n^2............... A202768.... A203475
2^(n-1)........... A203303.... A203477
2^n-1............. A203305.... A203479
n!................ A203306.... A203482
n(n+1)/2.......... A203309.... A203511
Fibonacci(n+1).... A203311.... A203518
prime(n).......... A080358.... A203521
odd prime(n)...... A203315.... A203524
nonprime(n)....... A203415.... A203527
composite(n)...... A203418.... A203530
2n-1.............. A108400.... A203516
n+floor(n/2)...... A203430
n+floor[(n+1)/2].. A203433
1/n............... A203421
1/(n+1)........... A203422
1/(2n)............ A203424
1/(2n+2).......... A203426
1/(3n)............ A203428
Generalizing, suppose that f(x,y) is a function of two variables and S=(s(1),s(2),...s(n)). The phrase, "Vandermonde sequence using f(x,y) applied to S" means the sequence a(n) whose n-th term is the product f(s(j,k)) : 1<=j...
If f(x,y) is a (bivariate) cyclotomic polynomial and S is a strictly increasing sequence of positive integers, then a(n) consists of integers, each of which divides its successor. Guide to sequences for which f(x,y) is x^2+xy+y^2 or x^2-xy+y^2 or x^2+y^2:
...
s(n) ............ x^2+xy+y^2.. x^2-xy+y^2.. x^2+y^2
n ............... A203012..... A203312..... A203475
n+1 ............. A203581..... A203583..... A203585
2n-1 ............ A203514..... A203587..... A203589
n^2 ............. A203673..... A203675..... A203677
2^(n-1) ......... A203679..... A203681..... A203683
n! .............. A203685..... A203687..... A203689
n(n+1)/2 ........ A203691..... A203693..... A203695
Fibonacci(n) .... A203742..... A203744..... A203746
Fibonacci(n+1) .. A203697..... A203699..... A203701
prime(n) ........ A203703..... A203705..... A203707
floor(n/2) ...... A203748..... A203752..... A203773
floor((n+1)/2) .. A203759..... A203763..... A203766
For f(x,y)=x^4+y^4, see A203755 and A203770. (End)

			a(4) = (1+2)*(1+3)*(1+4)*(2+3)*(2+4)*(3+4) = 12600.

Amarnath Murthy, Another combinatorial approach towards generalizing the AM-GM inequality, Octagon Mathematical Magazine, Vol. 8, No. 2, October 2000.
Amarnath Murthy, Smarandache Dual Symmetric Functions And Corresponding Numbers Of The Type Of Stirling Numbers Of The First Kind. Smarandache Notions Journal, Vol. 11, No. 1-2-3 Spring 2000.

T. D. Noe, Table of n, a(n) for n = 1..20

Cf. A006963, A093884, A203469.

a:= n-> mul(mul(i+j, i=1..j-1), j=2..n):
seq(a(n), n=1..12);  # Alois P. Heinz, Jul 23 2017

f[n_] := Product[(j + k), {k, 2, n}, {j, 1, k - 1}]; Array[f, 10] (* Robert G. Wilson v, Jan 08 2013 *)

A093883(n)=prod(i=1,n,(2*i-1)!/i!)  \\ M. F. Hasler, Nov 02 2012

Partial products of A006963: a(n) = Product((2*i-1)!/i!, i=1..n). - Vladeta Jovovic, May 27 2004
G.f.: G(0)/(2*x) -1/x, where G(k)= 1  + 1/(1 - 1/(1 + 1/((2*k+1)!/(k+1)!)/x/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, Jun 15 2013
a(n) ~ sqrt(A/Pi) * 2^(n^2 + n/2 - 7/24) * exp(-3*n^2/4 + n/2 - 1/24) * n^(n^2/2 - n/2 - 11/24), where A is the Glaisher-Kinkelin constant A074962. - Vaclav Kotesovec, Jan 26 2019

More terms from Vladeta Jovovic, May 27 2004

A203421 Reciprocal of Vandermonde determinant of (1,1/2,...,1/n).

Original entry on oeis.org

1, 1, -2, -18, 1152, 720000, -5598720000, -658683809280000, 1381360067999170560000, 59463021447701323327733760000, -59463021447701323327733760000000000000, -1542317635347398938581016812202229760000000000000

Offset: 0

Clark Kimberling, Jan 02 2012

Each term divides its successor, as in A000169.

G. C. Greubel, Table of n, a(n) for n = 0..35

Cf. A000169, A002109, A057077, A203422, A203424.

BarnesG:= func< n | (&*[Factorial(k): k in [0..n-2]]) >;
A203421:= func< n | (-1)^Binomial(n,2)*(Factorial(n))^n/BarnesG(n+2) >;
[A203421(n): n in [1..20]]; // G. C. Greubel, Dec 07 2023

(* First program *)
f[j_] := 1/j; z = 12;
v[n_] := Product[Product[f[k] - f[j], {j, 1, k - 1}], {k, 2, n}]
Table[v[n], {n, 1, z}]
1/%  (* A203421 *)
Table[v[n]/v[n + 1], {n, 1, z}]  (* A000169 signed *)
(* Additional programs *)
Table[(-1)^Floor[n/2]*Product[(k + 1)^k, {k, 0, n-1}], {n, 1, 10}] (* Vaclav Kotesovec, Oct 18 2015 *)
Table[(-1)^Binomial[n,2]*(n!)^n/BarnesG[n+2], {n, 20}] (* G. C. Greubel, Dec 07 2023 *)

a(n) = prod(i=2,n, (-i)^(i-1)); \\ Kevin Ryde, Apr 17 2022

def BarnesG(n): return product(factorial(k) for k in range(n-1))
def A203421(n): return (-1)^binomial(n, 2)*(gamma(n+1))^n/BarnesG(n+2)
[A203421(n) for n in range(1, 21)] # G. C. Greubel, Dec 07 2023

G.f.: G(0)/(2*x) -1/x, where G(k)= 1 + 1/(1 - x/(x + (2*k+1)/((2*k+1)^(2*k+1))/(1 + 1/(1 - x/(x - (2*k+2)/((2*k+2)^(2*k+2))/G(k+1)))))); (continued fraction). - Sergei N. Gladkovskii, Jun 03 2013
a(n) = (-1)^floor(n/2) * hyperfactorial(n)/n! = A057077(n) * A002109(n)/n!. - Paul J. Harvey, Feb 08 2014
a(n) = Product_{i=2..n} (-i)^(i-1). - Kevin Ryde, Apr 17 2022
abs(a(n)) ~ A * n^(n*(n-1)/2 - 5/12) / (sqrt(2*Pi) * exp(n^2/4 - n)), where A is the Glaisher-Kinkelin constant A074962. - Vaclav Kotesovec, Nov 20 2023
a(n) = (-1)^binomial(n,2) * (n!)^n / BarnesG(n+2). - G. C. Greubel, Dec 07 2023

a(0)=1 prepended by Alois P. Heinz, Apr 13 2024

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A203423 a(n) = w(n+1)/(2*w(n)), where w=A203422.

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A093883 Product of all possible sums of two distinct numbers taken from among first n natural numbers.

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A203421 Reciprocal of Vandermonde determinant of (1,1/2,...,1/n).

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