A074949 Denominators of Sum_{k=1..n} 1/lcm(n,k).

1, 1, 6, 6, 60, 60, 140, 420, 2520, 2520, 27720, 27720, 360360, 360360, 72072, 360360, 12252240, 12252240, 77597520, 46558512, 25865840, 33256080, 118982864, 5354228880, 8923714800, 3824449200, 80313433200, 80313433200, 2329089562800

Offset: 1

Author

Benoit Cloitre, Oct 05 2002

Keywords

• easy
• frac
• nonn

Examples

			1, 1, 5/6, 5/6, 37/60, 47/60, 69/140, 263/420, 1321/2520, 1429/2520, ...
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..2308

Crossrefs

Cf. A074947 (numerators).

Programs

Maple

A074949:=proc(n) local i: RETURN(denom(add(1/ilcm(n,i),i=1..n))): end; seq(A074949(n),n=1..30); # C. Ronaldo

Mathematica

a[n_] := Denominator @ Sum[1/LCM[k, n], {k, 1, n}]; Array[a, 30] (* Amiram Eldar, Jan 31 2021 *)

PARI

a(n)=denominator(sum(i=1,n,1/lcm(n,i)))