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Primes that cannot be represented as 2*p - q where p, q and 2*p^2 - q^2 are prime.
1

%I #8 Jul 18 2022 19:37:47

%S 2,3,5,13,17,37,61,137

%N Primes that cannot be represented as 2*p - q where p, q and 2*p^2 - q^2 are prime.

%C Conjecture: there are no other terms.

%e 11 is not in the sequence because 11 = 2*7 - 3 with 7, 3 and 2*7^2 - 3^2 = 89 prime.

%p M:= 10000: # to get all terms <= M

%p Pmax:= floor(M/(2-sqrt(2))):

%p Qmax:= floor(sqrt(2)*Pmax):

%p Q:= select(isprime,[2,seq(i,i=3..Qmax,2)]):

%p P:= select(`<=`,Q,Pmax): nQ:= nops(Q):

%p S:= convert(select(`<=`,P,M),set):

%p for p in P do

%p for j from 1 to nQ do

%p q:= Q[j];

%p r:= 2*p^2-q^2;

%p if r < 2 then break fi;

%p s:= 2*p-q;

%p if s <= M and isprime(r) and isprime(s) then S:= S minus {s} fi;

%p od od:

%p S;

%Y Cf. A355521.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Jul 05 2022