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A242773
The greater of twin primes p2 such that 2*p1 + p2 is a prime number (A174913) and also the lesser of other twin primes in A174913.
2
7, 11491, 32971, 33331, 33601, 42841, 58111, 93811, 96331, 114601, 180181, 273001, 309541, 334891, 401311, 540541, 633571, 717091, 784351, 820411, 870241, 879691, 907141, 948091, 989251, 991621, 994561, 1020961, 1028581, 1044751, 1185661, 1189651, 1245451, 1253911
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
FORMULA
a(n) = A242772(n) + 2.
EXAMPLE
a(1) = 7, 7 - 2 = 5 = A174913(1) and 2*A174913(1) + 7 = A174913(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