OFFSET
1,2
LINKS
Paul Larm (terms 1..20) and Amiram Eldar (terms 21..100), Table of n, a(n) for n = 1..100
Paul Larm, Table of a(n) for n = 2..25 showing prime factors.
FORMULA
a(1) = P(1)# - 1, a(2) = P(1)# + P(2)# -1; where P(n)# is the product of first n prime numbers (primorial#).
EXAMPLE
For n = 4, a(4) = 2 + 2*3 + 2*3*5 + 2*3*5*7 - 1 = 247.
MATHEMATICA
Accumulate[Denominator[Accumulate[1/Prime[Range[20]]]]] - 1 (* Alonso del Arte, Mar 21 2013 *)
Accumulate[Table[Fold[Times, Prime[Range[n]]], {n, 20}]]-1 (* Harvey P. Dale, May 23 2020 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paul Larm, Mar 21 2013
STATUS
approved