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

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

Offset

1,1

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

Formula

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

Mathematica

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

Prog

(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

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.

Sequence in context: A216179 A240804 A100277 * A080440 A159352 A289859

Adjacent sequences: A087395 A087396 A087397 * A087399 A087400 A087401

Keyword

nonn

Author

Cino Hilliard, Oct 21 2003

Extensions

Description corrected by Hugo Pfoertner, Jun 25 2004

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

Status

approved