A109923 a(n) = lcm(1,2,3,...,prime(n))/(1 + 2 + ... + prime(n)).

1, 4, 15, 420, 3960, 80080, 1225224, 19399380, 5354228880, 145568097675, 7600186994400, 254425307479200, 9957281351799600, 392482839950100900, 114779426083185063200, 5474978624167927514640, 312603618218620377448800

Offset

2,2

Links

Table of n, a(n) for n=2..18.

Formula

a(n) = A099795(n)/A006254(n-1). - Andrey Zabolotskiy, Mar 07 2018

a(n) = A056604(n)/A034953(n). - Michel Marcus, Mar 07 2018

Example

a(4)=15 because the 4th prime is 7 and lcm(1,2,3,4,5,6,7)/(1+2+3+4+5+6+7) = 420/28 = 15.

Maple

a:=n->lcm(seq(i, i=1..ithprime(n)))/sum(j, j=1..ithprime(n)): seq(a(n), n=2..20); # Emeric Deutsch, Jul 16 2005

Prog

(PARI) a(n) = lcm(vector(prime(n), k, k))/sum(k=1, prime(n), k); \\ Michel Marcus, Mar 07 2018

Crossrefs

Cf. A006254, A034953, A056604, A099795, A109922.

Sequence in context: A363351 A000881 A354462 * A006524 A299683 A341598

Adjacent sequences: A109920 A109921 A109922 * A109924 A109925 A109926

Keyword

easy,nonn

Author

Amarnath Murthy, Jul 16 2005

Extensions

More terms from Emeric Deutsch, Jul 16 2005

Status

approved