A117472 Values of c in a^2 + b^2 = c^2, where b - a = 17 and gcd(a,b,c)=1.

25, 53, 137, 305, 797, 1777, 4645, 10357, 27073, 60365, 157793, 351833, 919685, 2050633, 5360317, 11951965, 31242217, 69661157, 182092985, 406014977, 1061315693, 2366428705, 6185801173, 13792557253, 36053491345

Offset

1,1

Comments

b - a = 17 is the third term in A058529 The values of 'a' are defined by A117473

Links

Table of n, a(n) for n=1..25.

Index entries for linear recurrences with constant coefficients, signature (0,6,0,-1).

Formula

c(1)=25, c(2)=53, c(3)=137, c(4)=305, c(n) = 6*c(n-2) - c(n-4), if c > 4

G.f.: -x*(13*x^3+13*x^2-53*x-25) / ((x^2-2*x-1)*(x^2+2*x-1)). [Colin Barker, Dec 17 2012]

Example

c(5) = 6*137 - 25 = 797
555*555 + 572*572 = 797*797, where 572-555 = 17 and gcd(555,572,797)=1

Crossrefs

Cf. A117473, A058529.

Sequence in context: A043235 A044015 A118304 * A146633 A123825 A349416

Adjacent sequences: A117469 A117470 A117471 * A117473 A117474 A117475

Keyword

nonn,easy

Author

Andras Erszegi (erszegi.andras(AT)chello.hu), Mar 19 2006

Status

approved