A124981 Odd numbers that are not the sum of 2 squares.

3, 7, 11, 15, 19, 21, 23, 27, 31, 33, 35, 39, 43, 47, 51, 55, 57, 59, 63, 67, 69, 71, 75, 77, 79, 83, 87, 91, 93, 95, 99, 103, 105, 107, 111, 115, 119, 123, 127, 129, 131, 133, 135, 139, 141, 143, 147, 151, 155, 159, 161, 163, 165, 167, 171, 175, 177, 179, 183, 187

Offset: 1

Author

Artur Jasinski, Nov 15 2006

Keywords

• nonn

Examples

			13 is not in the list because it can be written as 3^2+2^2.
		

Links

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

Crossrefs

Cf. A005408, A022544.

Programs

Mathematica

Select[2 * Range[0, 100] + 1, SquaresR[2, #] == 0 &] (* Amiram Eldar, Mar 12 2020 *)

PARI

isA022544(n)={ local(cnt=0,y2) ; for(x=0,floor(sqrt(n)), y2=n-x^2 ; if( y2>=x^2 && issquare(y2), return(0) ; ) ; ) ; return(1) ; } isA124981(n)={ return( (n%2) && isA022544(n)) ; } { for(n=1,200, if( isA124981(n), print1(n,", ") ; ) ; ) ; } \\ R. J. Mathar, Nov 29 2006

Formula

Equals A022544 INTERSECT A005408. - R. J. Mathar, Nov 29 2006

Extensions

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