A217723 a(n) = (sum of first n primorial numbers) minus 1.
1, 7, 37, 247, 2557, 32587, 543097, 10242787, 233335657, 6703028887, 207263519017, 7628001653827, 311878265181037, 13394639596851067, 628284422185342477, 33217442899375387207, 1955977793053588026277, 119244359152460559009547
Offset: 1
Examples
For n = 4, a(4) = 2 + 2*3 + 2*3*5 + 2*3*5*7 - 1 = 247.
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.
Programs
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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 *)
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#).