A088411 A088257 indexed by A002110.

0, 1, 2, 3, 4, 5, 6, 11, 13, 24, 66, 68, 75, 167, 171, 172, 287, 310, 352, 384, 457, 564, 590, 616, 620, 643, 849, 1391, 1552, 1613, 1849, 2122, 2647, 2673, 4413, 13494, 31260, 33237, 67132, 85586, 234725

Offset

1,3

Comments

Union of A057704 and A014545. - Jeppe Stig Nielsen, Aug 01 2019

Links

Table of n, a(n) for n=1..41.

Formula

a(n)=k such that A088257(n)=A002110(k).

Example

3 is in the sequence because primorial p_3# = 2 * 3 * 5 = 30 has two prime neighbors 29 and 31.
4 is in the sequence because primorial p_4# = 2 * 3 * 5 * 7 = 210 has one prime neighbor 211; 209 = 11 * 19.
7 is not in the sequence because the product of the smallest 7 primes has two composite neighbors.

Maple

A:= NULL:
P:= 1: p:= 1;
for n from 1 to 700 do
  p:= nextprime(p);
  P:= P*p;
  if isprime(P+1) or isprime(P-1) then A:= A, n fi
od:
A; # Robert Israel, Aug 03 2016

Mathematica

Select[Range[0, 600], Total@ Boole@ PrimeQ@ {# - 1, # + 1} > 0 &@ Apply[Times, Prime@ Range@ #] &] (* Michael De Vlieger, Aug 03 2016 *)

Prog

(PARI) is(k)=pr=prod(j=1, k, prime(j)); ispseudoprime(pr-1)||ispseudoprime(pr+1) \\ Jeppe Stig Nielsen, Aug 01 2019

Crossrefs

Cf. A002110, A088257, A014545, A057704.

Sequence in context: A108378 A084588 A309548 * A075073 A157420 A221471

Adjacent sequences: A088408 A088409 A088410 * A088412 A088413 A088414

Keyword

nonn,more

Author

Ray Chandler, Sep 29 2003

Extensions

a(22)-a(27) from Michael De Vlieger, Aug 03 2016

a(28)-a(40) from Jeppe Stig Nielsen, Aug 01 2019

a(41) from Jeppe Stig Nielsen, Oct 19 2021

Status

approved