OFFSET
1,1
COMMENTS
It seems that a(n) == 1 mod 10 for n > 1.
a(n) == 1 (mod 10) for n > 1 since if p2 == 3, 7 or 9 (mod 10) then 2*p1 + p2, p1, or 2*p1 + p2 + 2 is divisible by 5, respectively. - Amiram Eldar, Dec 31 2019
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A242772(n) + 2.
MATHEMATICA
Select[Range[10^6], And @@ PrimeQ[{#, # + 2, (p = 3*# + 2), p + 2, 3*p + 2}] &] + 2 (* Amiram Eldar, Dec 31 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Ivan N. Ianakiev, May 22 2014
STATUS
approved