A087400 Primes p such that p+2 is a piptorial number. Also numbers such that A080696(n)- 2 is prime.

13, 163, 2803, 3565153, 210344143, 86915972211813115391953, 4419764102942908730796303703, 114681479899746991802547357477494803

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

Links

Table of n, a(n) for n=1..8.

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

Cf. A080696, A090886.

Sequence in context: A212785 A133180 A090134 * A012828 A119539 A277412

Adjacent sequences: A087397 A087398 A087399 * A087401 A087402 A087403

Keyword

nonn

Author

Cino Hilliard, Oct 21 2003

Status

approved