A329498 Denominator of the rational number alpha_n involved in the calculation of the second moment of the n-th term of Ulam's "history-dependent random sequence".

1, 1, 2, 6, 24, 120, 720, 1680, 40320, 362880, 725760, 7983360, 2128896, 113218560, 387459072, 261534873600, 836911595520, 71137485619200, 75322043596800, 1621934672117760, 37429261664256000, 10218188434341888000, 224800145555521536000

Offset: 1

Author

N. J. A. Sloane, Nov 17 2019

Keywords

• nonn
• frac

Examples

			0, 2, 21/2, 223/6, 2603/24, 33623/120, 477977/720, 2474153/1680, ...
		

Links

• Mark Kac, A history-dependent random sequence defined by Ulam, Advances in Applied Mathematics 10.3 (1989): 270-277. See page 273, sigma_k and alpha_k.

Crossrefs

Cf. A329495, A329496, A327497.

Programs

Maple

s:=[1]; a:=[0];
for N from 2 to 40 do # N = n+1
n:=N-1;
t1:=s[n]+(1/n)*add(s[k],k=1..n)+2*s[n]/n+(2/n)*a[n];
t2:=s[n]+(1/n)*add(s[k],k=1..n)+a[n]+(2/n)*add(a[k],k=1..n);
s:=[op(s),t1];
a:=[op(a),t2];
od:
s; # sigma_n
a; # alpha_n
sn:=map(numer,s); # A329495
sd:=map(denom,s); # A329496
an:=map(numer,a); # A329497
ad:=map(denom,a); # A329498