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a(n) = lcm(1,2,3,...,prime(n))/(1 + 2 + ... + prime(n)).
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%I #12 Mar 07 2018 06:23:14

%S 1,4,15,420,3960,80080,1225224,19399380,5354228880,145568097675,

%T 7600186994400,254425307479200,9957281351799600,392482839950100900,

%U 114779426083185063200,5474978624167927514640,312603618218620377448800

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

%F a(n) = A099795(n)/A006254(n-1). - _Andrey Zabolotskiy_, Mar 07 2018

%F a(n) = A056604(n)/A034953(n). - _Michel Marcus_, Mar 07 2018

%e 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.

%p 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

%o (PARI) a(n) = lcm(vector(prime(n), k, k))/sum(k=1, prime(n), k); \\ _Michel Marcus_, Mar 07 2018

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

%K easy,nonn

%O 2,2

%A _Amarnath Murthy_, Jul 16 2005

%E More terms from _Emeric Deutsch_, Jul 16 2005