A185313 - OEIS

%I #25 Jun 07 2017 09:36:22

%S 2,2,5,5,5,17,17,53507,364187,155650237,15644021363,604394270371,

%T 767783880089

%N Start of a sequence of n consecutive primes such that the sum of any three consecutive members is also prime.

%C a(14) > 1.8*10^14. - _Giovanni Resta_, Jun 07 2017

%e Vacuously, the sum of every three consecutive members of {2, 3} is prime, so a(2) = 2.  a(4) = 5 because 5 + 7 + 11 and 7 + 11 + 13 are prime.

%o (PARI) a(n)=if(n<3,return(2),n-=2);my(len=0,p=2,q=3);forprime(r=5,default(primelimit),if(isprime(p+q+r),if(len++==n,my(t=p);for(i=2,n,t=precprime(t-1));return(t)),len=0);p=q;q=r) \\ _Charles R Greathouse IV_, Feb 08 2012

%Y Cf. A072225.

%K nonn,more

%O 1,1

%A _Charles R Greathouse IV_, Feb 08 2012

%E a(11) from _Charles R Greathouse IV_, Feb 10 2012

%E a(12) from _Charles R Greathouse IV_, Feb 12 2012

%E a(13) from _Zak Seidov_, Jun 03 2017