A309812 Odd integers k such that k^2 is arithmetic mean of two other perfect squares.
5, 13, 15, 17, 25, 29, 35, 37, 39, 41, 45, 51, 53, 55, 61, 65, 73, 75, 85, 87, 89, 91, 95, 97, 101, 105, 109, 111, 113, 115, 117, 119, 123, 125, 135, 137, 143, 145, 149, 153, 155, 157, 159, 165, 169, 173, 175, 181, 183, 185, 187, 193, 195, 197, 203, 205, 215, 219
Offset: 1
Keywords
Examples
5 is a term because 5^2 = 25 = (1^2 + 7^2)/2.
Programs
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Mathematica
Select[Range[1, 300, 2], SquaresR[2, 2 #^2] > 4 &] (* Giovanni Resta, Aug 18 2019 *)
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PARI
isok(n) = {if (n %2, for (i=1, n, x = 2*n^2-i^2; if ((x!=i^2) && (x>0) && issquare(x), return (i));););} \\ Michel Marcus, Aug 18 2019
Extensions
More terms from Giovanni Resta, Aug 18 2019