A356890 a(n) is the first twin prime that begins a sequence of exactly n twin primes under the map t -> 3*t+2.

7, 3, 19, 40951819, 12454922269

Offset

1,1

Links

Table of n, a(n) for n=1..5.

Example

a(3) = 19 because 19 is a twin prime, 3*19+2 = 59 is a twin prime, and 3*59+2 = 179 is a twin prime, but 3*179+2 = 539 is not a twin prime.

Maple

f:= proc(p) local q; option remember;
    if isprime(p) and isprime(p + 4*(p mod 3) - 6) then
       1 + procname(3*p+2)
    else 0
    fi
end proc:
f(3):= 2:
A:= Vector(4): count:= 0:
for p from 5 by 2 while count < 4 do
  v:= f(p);
  if v > 0  and A[v] = 0 then A[v]:= p; fi
od:
convert(A, list);

Crossrefs

Sequence in context: A357200 A284477 A145399 * A160797 A050013 A161417

Adjacent sequences: A356887 A356888 A356889 * A356891 A356892 A356893

Keyword

nonn,more

Author

J. M. Bergot and Robert Israel, Sep 02 2022

Extensions

a(5) from Jean-Marc Rebert, Sep 08 2022

Status

approved