A092474 a(n) is the first term in a sequence of primes such that a(n)+4m^2 is also prime for m = 1 to n.

3, 3, 7, 7, 7, 7, 37, 37, 163, 163, 163, 163, 163, 163, 163, 163, 163, 163, 163

Offset: 1

Author

Ray G. Opao, Mar 25 2004

Keywords

• nonn

Comments

a(1) starts sequence A023200; a(2) starts sequence A049492. (I've searched up to 2000000 but haven't yet found the terms from a(20) onward.)

Examples

			a(5) = 7.
7+4(1^2) = 7+4(1) = 7+4 = 11 which is prime.
7+4(2^2) = 7+4(4) = 7+16 = 23 which is prime.
7+4(3^2) = 7+4(9) = 7+36 = 43 which is prime.
7+4(4^2) = 7+4(16) = 7+64 = 71 which is prime.
7+4(5^2) = 7+4(25) = 7+100 = 107 which is prime.
		

Programs

Mathematica

Flatten[Table[Select[Prime[Range[100]],And@@PrimeQ[Table[#+4n^2,{n,i}]]&,1],{i,19}]] (* Harvey P. Dale, Oct 04 2012 *)