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A088256 Primorial numbers k such that both k-1 and k+1 are prime. 4
6, 30, 2310 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: sequence is finite.

No more terms in the first 300 primorials. - David Wasserman, Jul 25 2005

Search extended to first 700 primorials by Michael De Vlieger, Aug 31 2016

Intersection of A014574 and A002110. - Michel Marcus, Dec 03 2016

LINKS

Table of n, a(n) for n=1..3.

EXAMPLE

210 = primorial(4) is not a member as 209 is composite.

MAPLE

f:= proc(n)

  local P;

  P:= mul(seq(ithprime(i), i=1..n));

  if isprime(P+1) and isprime(P-1) then P else NULL fi

end proc:

map(f, [$1..300]); # Robert Israel, Aug 31 2016

MATHEMATICA

Select[Times @@ # & /@ Prime@ Range@ Range@ 700, Times @@ Boole@ PrimeQ@ {# - 1, # + 1} == 1 &] (* Michael De Vlieger, Aug 31 2016 *)

PROG

(PARI) lista(nn) = for (n=1, nn, pr = prod(i=1, n, prime(i)); if (isprime(pr-1) && isprime(pr+1), print1(pr, ", "))); \\ Michel Marcus, Aug 31 2016

CROSSREFS

Cf. A001097, A002110, A088257, A014574, A119411, A136349.

Sequence in context: A222718 A200894 A202861 * A136349 A119411 A036285

Adjacent sequences:  A088253 A088254 A088255 * A088257 A088258 A088259

KEYWORD

more,nonn,bref

AUTHOR

Amarnath Murthy, Sep 27 2003

EXTENSIONS

Corrected by Ray Chandler, Sep 28 2003

STATUS

approved

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Last modified July 18 10:35 EDT 2019. Contains 325138 sequences. (Running on oeis4.)