A124982 Nonprime numbers with a unique partition as a sum of 2 squares x^2 + y^2.

0, 1, 4, 8, 9, 10, 16, 18, 20, 26, 32, 34, 36, 40, 45, 49, 52, 58, 64, 68, 72, 74, 80, 81, 82, 90, 98, 104, 106, 116, 117, 121, 122, 128, 136, 144, 146, 148, 153, 160, 162, 164, 178, 180, 194, 196, 202, 208, 212, 218, 226, 232, 234, 242, 244, 245, 256, 261, 272, 274

Offset: 1

Author

Artur Jasinski, Nov 16 2006

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000161, A002145.

Programs

Mathematica

Select[Range[0, 300], !PrimeQ[#] && Length @ PowersRepresentations[#, 2, 2] == 1 &] (* Amiram Eldar, Mar 12 2020 *)

PARI

A000161(n)={ local(cnt=0,y2) ; for(x=0,floor(sqrt(n)), y2=n-x^2 ; if( y2>=x^2 && issquare(y2), cnt++ ; ) ; ) ; return(cnt) ; } isA124982(n)= { if( isprime(n), return(0), if(A000161(n)==1, return(1), return(0) ) ) ; } { for(n=0,300, if( isA124982(n), print1(n,", ") ; ) ; ) ; } \\ R. J. Mathar, Nov 29 2006

Formula

A000161(a(n)) = 1. - R. J. Mathar, Nov 29 2006

Extensions

Corrected and extended by R. J. Mathar, Nov 29 2006