OFFSET
1,2
COMMENTS
a(n) is the least k such that (2*n-1)^2+4*k is prime but (2*m-1)^2+4*k is composite for all m from 1 to n-1.
EXAMPLE
a(4) = 6 because 2*4-1 = 7 and 7^2+4*6 = 73 is prime but 1^2+4*6 = 25, 3^2+4*6 = 33 and 5^2+4*6=49 are not.
MAPLE
f:= proc(n) local k, m;
m:= 4*n;
for k from 1 by 2 do
if isprime(k^2+m) then return k fi
od
end proc:
V:= Vector(119):
count:= 0:
for n from 1 while count < 60 do
v:= f(n);
if v <= 119 and V[v]=0 then V[v]:= n; count:= count+1 fi
od:
seq(V[2*i-1], i=1..60);
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert Israel, Jun 20 2021
STATUS
approved