login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A088256 Primorial numbers k such that both k-1 and k+1 are prime. 4

%I

%S 6,30,2310

%N Primorial numbers k such that both k-1 and k+1 are prime.

%C Conjecture: sequence is finite.

%C No more terms in the first 300 primorials. - _David Wasserman_, Jul 25 2005

%C Search extended to first 700 primorials by _Michael De Vlieger_, Aug 31 2016

%C Intersection of A014574 and A002110. - _Michel Marcus_, Dec 03 2016

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

%p f:= proc(n)

%p local P;

%p P:= mul(seq(ithprime(i),i=1..n));

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

%p end proc:

%p map(f, [$1..300]); # _Robert Israel_, Aug 31 2016

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

%o (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

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

%K more,nonn,bref

%O 1,1

%A _Amarnath Murthy_, Sep 27 2003

%E Corrected by _Ray Chandler_, Sep 28 2003

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 26 01:34 EDT 2019. Contains 326324 sequences. (Running on oeis4.)