A090788 Numbers that can be expressed as the difference of the squares of primes in just two distinct ways.

72, 360, 432, 528, 768, 888, 960, 1032, 1080, 1128, 1272, 1392, 1488, 1512, 1608, 1632, 1728, 1920, 2088, 2112, 2232, 2352, 2400, 2448, 2568, 2688, 2808, 3048, 3168, 3240, 3288, 3480, 3648, 3768, 4008, 4032, 4128, 4248, 4272, 4392, 4488, 4512, 4992

Offset: 1

Author

Ray Chandler, Feb 14 2004

Keywords

• nonn

Examples

			72 = 11^2 - 7^2 = 19^2 - 17^2.
		

Crossrefs

Cf. A078667, A090781, A090782.

Programs

PARI

i=4; while(i<=5000, k=0; m=2; while(m*m<=i, if(i%(2*m)==0, a=(i/m-m)/2; b=a+m; if(isprime(a)&&isprime(b), k+=1)); m+=2); if(k==2, print1(i, ", ")); i+=4) \\ Antonio Roldán, Nov 06 2018