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

1,2

Comments

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

Links

Table of n, a(n) for n=1..61.

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

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]&]

Crossrefs

Cf. A005471, A175281.

Sequence in context: A075663 A325419 A139212 * A127875 A056231 A248637

Adjacent sequences: A175279 A175280 A175281 * A175283 A175284 A175285

Keyword

nonn

Author

Zak Seidov, Mar 21 2010

Status

approved