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A070826 One half of product of first n primes A000040. 42
1, 3, 15, 105, 1155, 15015, 255255, 4849845, 111546435, 3234846615, 100280245065, 3710369067405, 152125131763605, 6541380665835015, 307444891294245705, 16294579238595022365, 961380175077106319535, 58644190679703485491635, 3929160775540133527939545, 278970415063349480483707695 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Also, with offset 0, product of first n odd primes. - N. J. A. Sloane, Feb 26 2017

Identical to A002110(n)/2, n>=1.

a(n+1) is the least odd number with exactly n distinct prime divisors. - Labos Elemer, Mar 24 2003

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..200

FORMULA

a(n) = (1/2)*product(p(n), n=1..n) with p(n) := A000040(n).

MAPLE

with (numtheory):a:=n->mul(ithprime(j), j=2..n):seq(a(n), n=1..17); # Zerinvary Lajos, Aug 24 2008

MATHEMATICA

Rest[ FoldList[ Times, 1, Prime[ Range[ 18]] ]]/2 (* Robert G. Wilson v, Feb 17 2004 *)

FoldList[Times, 1, Prime[Range[2, 18]]] (* Zak Seidov, Jan 26 2009 *)

PROG

(PARI) a(n) = prod(k=1, n, prime(k))/2; \\ Michel Marcus, Mar 25 2017

CROSSREFS

Cf. A003266 (for Fibonacci), A070825 (for Lucas), A003046 (for Catalan).

Cf. also A002110, A091852.

Range of A196529.

Sequence in context: A000268 A207818 A118750 * A048599 A129731 A269455

Adjacent sequences:  A070823 A070824 A070825 * A070827 A070828 A070829

KEYWORD

nonn,easy

AUTHOR

Wolfdieter Lang, May 10 2002

EXTENSIONS

Formula corrected by Gary Detlefs, Dec 07 2011

a(18)-a(20) from Vincenzo Librandi, Mar 25 2017

STATUS

approved

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Last modified June 25 19:53 EDT 2017. Contains 288729 sequences.