OFFSET
0,1
COMMENTS
If a(n) > -1 then a(n) >= A359439(n).
a(22) <= 10228945815339008; a(23) <= 188039754665689088; a(24) <= 54409680373415936; a(25) <= 246561971023904768; a(26) <= 966464636658384896. - Daniel Suteu, Jan 05 2023
EXAMPLE
a(4) = 48 = 3*2^4 = 5^2 + 5^2 - 2.
MAPLE
f:= proc(n) local b, t, s, x, y;
t:= 2^n; b:= 2;
do
b:= nextprime(b);
if member(3, numtheory:-factorset(b*t+2) mod 4) then next fi;
if ormap(s -> isprime(subs(s, x)) and isprime(subs(s, y)), [isolve(x^2+y^2-2=b*t)]) then return b*t fi
od;
end proc:
f(2):= -1:
map(f, [$0..18]);
CROSSREFS
KEYWORD
sign,more
AUTHOR
Robert Israel, Jan 02 2023
EXTENSIONS
a(19)-a(21) from Daniel Suteu, Jan 05 2023
STATUS
approved