A096831 -id:A096831 - cp's OEIS frontend

A096832 Number of primes in enlarged neighborhood with center = n-th primorial and radius = 2*ceiling(log(n-th primorial)). So compared to A096831, the radius is doubled.

2, 4, 4, 2, 3, 4, 1, 2, 1, 1, 1, 1, 3, 3, 1, 4, 2, 1, 4, 1, 2, 4, 1, 7, 1, 4, 2, 3, 0, 2, 3, 3, 0, 1, 6, 2, 1, 2, 4, 2, 3, 2, 2, 0, 3, 0, 2, 5, 3, 3, 1, 5, 2, 6, 3, 4, 3, 2, 2, 4, 2, 4, 1, 4, 7, 5, 2, 7, 1, 3, 2, 2, 6, 6, 3, 1, 3, 5, 4, 1, 4, 5, 6, 2, 5, 2, 4, 2, 0, 6, 1, 3, 5, 2, 5, 4, 4, 4, 3, 4, 3, 1, 3, 2, 4

Offset: 1

Labos Elemer, Jul 14 2004

nonn

What is exceptional in such neighborhoods of primorials is that in most cases no primes occur, i.e., these zones are peculiarly poor or empty of primes! If the radius is doubled then the density of primes appears to be "normal".

			n=7: 7th primorial = 510510; for radius=14, no primes in the relevant neighborhood; for radius=28, then one prime appears: 510529.

Cf. A096509-A096523, A096830-A096840; A002110.

A333058 0, 1, or 2 primes at primorial(n) +- 1.

Original entry on oeis.org

1, 1, 2, 2, 1, 2, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

Offset: 0

Frank Ellermann, Mar 06 2020

nonn

a(n) = 0 marks a prime gap size of at least 2*prime(n+1)-1, e.g., primorial(8) +- prime(9) = {9699667,9699713} are primes, gap 2*23-1.
Mathworld reports that it is not known if there are an infinite number of prime Euclid numbers.
The tables in Ondrejka's collection contain no further primorial twin primes after {2309,2311} = primorial(13) +- 1 up to primorial(15877) +- 1 with 6845 digits.

			a(2) = a(3) = a(5) = 2: 2*3 +-1 = {5,7}, 6*5 +-1 = {29,31} and 210*11 +-1 = {2309,2311} are twin primes.
a(1) = a(4) = a(6) = 1: 1, 30*7 - 1 = 209 and 2310*13 + 1 = 30031 are not primes.
a(7) = 0: 510509 = 61 * 8369 and 510511 = 19 * 26869 are not primes.

H. Dubner, A new primorial prime, J. Rec. Math., 21 (No. 4, 1989), 276.

Chris K. Caldwell, the top 20: Primorial, 2012.
H. Dubner & N. J. A. Sloane, Correspondence, 1991, on A005234.
G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 30029.
G. L. Honaker, Jr. and Chris Caldwell, Prime Curios! 9699667.
Rudolf Ondrejka, The Top Ten: a Catalogue of Primal Configurations, 2001, tables 20, 20A, 20B.
Eric Weisstein's World of Mathematics, Primorial Prime.
Eric Weisstein's World of Mathematics, Euclid Number.

Cf. A096831, A002110 (primorials, p#), A057706.
Cf. A006862 (Euclid, p#+1), A005234 (prime p#+1), A014545 (index prime p#+1).
Cf. A057588 (Kummer, p#-1), A006794 (prime p#-1), A057704 (index prime p#-1).
Cf. A010051, A088411 (where a(n) is positive), A088257.

p:= proc(n) option remember; `if`(n<1, 1, ithprime(n)*p(n-1)) end:
a:= n-> add(`if`(isprime(p(n)+i), 1, 0), i=[-1, 1]):
seq(a(n), n=0..120);  # Alois P. Heinz, Mar 18 2020

primorial[n_] := primorial[n] = Times @@ Prime[Range[n]];
a[n_] := Boole@PrimeQ[primorial[n] - 1] + Boole@PrimeQ[primorial[n] + 1];
a /@ Range[0, 105] (* Jean-François Alcover, Nov 30 2020 *)

S = ''                     ;  Q = 1
do N = 1 to 27
   Q = Q * PRIME( N )
   T = ISPRIME( Q - 1 ) + ISPRIME( Q + 1 )
   S = S || ',' T
end N
S = substr( S, 3 )
say S                      ;  return S

a(n) = [ isprime(primorial(n) - 1) ] + [ isprime(primorial(n) + 1) ].

a(n) = Sum_{i in {-1,1}} A010051(primorial(n) + i).

cp's OEIS Frontend

A096832 Number of primes in enlarged neighborhood with center = n-th primorial and radius = 2*ceiling(log(n-th primorial)). So compared to A096831, the radius is doubled.

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A333058 0, 1, or 2 primes at primorial(n) +- 1.

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