A087398 Primes of the form primorial(P(k))/2-2.

13, 103, 1153, 15013, 255253, 4849843, 111546433, 100280245063, 152125131763603, 16294579238595022363, 278970415063349480483707693, 11992411764462614086353260819346129198103, 481473710367991963528473107950567214598209565303106537707981745633

Offset: 1

Author

Cino Hilliard, Oct 21 2003

Keywords

• nonn

Comments

Twinmorial numbers are the partial products of twin primes. Sum of reciprocals = 0.08756985926348207565388288916..

The next term (a(14)) has 174 digits. - Harvey P. Dale, Mar 30 2013

Links

• Charles R Greathouse IV, Table of n, a(n) for n = 1..19

Crossrefs

Cf. A096177 primes k such that primorial(k)/2+2 is prime, A096178 primes of the form primorial(k)/2+2, A096547 Primes k such that primorial(k)/2-2 is prime, A067024 smallest p+2 that has n distinct prime factors, A014545 primorial primes.

Programs

Mathematica

Select[#/2-2&/@Rest[FoldList[Times,1,Prime[Range[100]]]],PrimeQ] (* Harvey P. Dale, Mar 30 2013 *)

PARI

twimorial(n) = { s=0; p=3; forprime(x=5,n, if(isprime(x-2),c1++); p=p*x; if(isprime(p-2), print1(p-2","); c2++; s+=1.0/(p-2); ) ); print(); print(s) }

PARI

v=[];pr=1; forprime(p=3,2357,pr*=p; if(ispseudoprime(pr-2),v=concat(v,pr-2))) \\ Charles R Greathouse IV, Feb 14 2011

Formula

Twins 3*5 = 15 = p+2. p=13.

Extensions

Description corrected by Hugo Pfoertner, Jun 25 2004

One more term (a(13)) added by Harvey P. Dale, Mar 30 2013