The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A070826 One half of product of first n primes A000040. 81
 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) = A002110(n)/2. From Antti Karttunen, Feb 06 2024: (Start) a(1) = 1, and for n > 1, a(n) = A276086(A060389(n-1)). a(n) = A024451(n) - 2*A203008(n-1). (End) MAPLE 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 (Python) from sympy import primorial def A070826(n): return primorial(n)>>1 # Chai Wah Wu, Jul 21 2022 CROSSREFS Cf. A003266 (for Fibonacci), A070825 (for Lucas), A003046 (for Catalan). Cf. also A002110, A024451, A060389, A091852, A276086, A203008 [= A003415(a(1+n))]. Range of A196529. Sequence in context: A207818 A354218 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 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 7 01:21 EDT 2024. Contains 375002 sequences. (Running on oeis4.)