OFFSET
1,1
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..185
Ronald K. Hoeflin, Titan Test.
FORMULA
From Amiram Eldar, Nov 15 2020: (Start)
Sum_{n>=1} 1/a(n) = A139395.
MATHEMATICA
terms=20; With[{prs=Prime[Range[(terms(terms+1))/2]]}, Table[ Times@@ Take[prs, {(n(n-1))/2+1, (n(n+1))/2}], {n, terms}]] (* Harvey P. Dale, Aug 06 2013 *)
With[{nn=40}, Times@@@TakeList[Prime[Range[(nn(nn+1))/2]], Range[nn]]] (* Requires Mathematica version 11 or later *) (* Harvey P. Dale, Jan 15 2020 *)
PROG
(PARI) a(n)=my(s=1); forprime(p=prime(n*(n-1)/2+1), prime(n*(n+1)/2), s*=p); s \\ Charles R Greathouse IV, Aug 06 2013
(Python)
from math import prod
from sympy import prime
def a(n): return prod(prime(i) for i in range((n-1)*n//2+1, n*(n+1)//2+1))
print([a(n) for n in range(1, 14)]) # Michael S. Branicky, Feb 15 2021
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
EXTENSIONS
Corrected and extended by Harvey P. Dale, Aug 06 2013
STATUS
approved