The Ulam spiral with display of the first twin prime numbers ('2-twin' prime numbers) [La spirale d'Ulam montrant les premiers nombres premiers jumeaux (nombres premiers '2-jumeaux')].
Starting from the center of the picture -red square-, all the little squares (even the black ones) are
numbered (N=1, 2, 3,...) when following a square spiral.
A '2-twin' prime number pair is a set of two prime numbers {P1,P2} such that on the one
hand P2-P1=2 and on the other hand there are no prime number between P1 and P2.
The yellow squares display the first '2-twin' prime number pairs (light yellow for P2 and dark yellow for P1).
A famous conjecture states that there are infinitely many '2-twin' prime number pairs
{2,3,5,7,11,13,17,19,23,29,31,37,41,... (INFINITY?)}.
See the Ulam spiral:
See the 'N-twin' prime numbers (with N=2,4,6,8 respectively):