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

1,1

Links

Table of n, a(n) for n=1..43.

Example

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

Prog

(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

Crossrefs

Cf. A078667, A090781, A090782.

Sequence in context: A157909 A107314 A223472 * A334902 A192792 A303621

Adjacent sequences: A090785 A090786 A090787 * A090789 A090790 A090791

Keyword

nonn

Author

Ray Chandler, Feb 14 2004

Status

approved