OFFSET
1,1
COMMENTS
Piptorial numbers are the partial products of prime-indexed primes.
Sum of reciprocals = 0.08341509210884323904648676616...
a(9) = A080696(1111) - 2 = 1.0954...*10^4885. - Amiram Eldar, Jul 05 2024
EXAMPLE
(Product of first four pips) - 2 = 3*5*11*17 - 2 = 2805 - 2 = 2803, which is prime, so 2803 is in the sequence.
MATHEMATICA
seq[kmax_] := Module[{r = 1, p = 1, s = {}}, Do[p = NextPrime[p]; r *= Prime[p]; If[PrimeQ[r - 2], AppendTo[s, r - 2]], {k, 1, kmax}]; s]; seq[20] (* Amiram Eldar, Jul 05 2024 *)
PROG
(PARI) piptorial(n) = { s=0; p=1; for(x=1, n, p=p*prime(prime(x)); if(isprime(p-2), print1(p-2", "); s+=1.0/(p-2)) ); print(); print(s) }
CROSSREFS
KEYWORD
nonn
AUTHOR
Cino Hilliard, Oct 21 2003
STATUS
approved