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A087398
Primes of the form primorial(P(k))/2-2.
4
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
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