A175282 Positive numbers n with property that n^2+3n+9 is prime (A005471).

1, 2, 4, 7, 8, 10, 11, 16, 17, 23, 25, 28, 29, 31, 32, 37, 38, 43, 49, 50, 56, 58, 64, 70, 73, 85, 88, 91, 94, 95, 98, 101, 107, 112, 121, 122, 127, 130, 133, 134, 136, 140, 142, 143, 155, 158, 163, 164, 169, 172, 175, 176, 179, 182, 197, 200, 205, 206, 212, 214, 218

Offset: 1

Author

Zak Seidov, Mar 21 2010

Keywords

• nonn

Comments

Notice that at n=-1, n^2+3n+9=7 is also (positive) prime.

Links

• Erik Dofs, Solutions of x^3+y^3+z^3=n*x*y*z, Acta Arithm. 73.3 (1995) 201

Crossrefs

Cf. A005471, A175281.

Programs

Maple

A175282 := proc(n)
    option remember;
    if n = 1 then
        1;
    else
        for a from procname(n-1)+1 do
            if isprime(a^2+3*a+9) then
                return a;
            end if;
        end do;
    end if;
end proc: # R. J. Mathar, Jun 06 2019

Mathematica

Select[Range[1,400],PrimeQ[ #^2+3*#+9]&]