A117476 The values of a in a^2 + b^2 = c^2 where b - a = 23 and gcd(a,b,c)=1.

12, 33, 133, 252, 832, 1525, 4905, 8944, 28644, 52185, 167005, 304212, 973432, 1773133, 5673633, 10334632, 33068412, 60234705, 192736885, 351073644, 1123352944, 2046207205, 6547380825, 11926169632, 38160932052, 69510810633

Offset

1,1

Comments

Values of c are in A117475

Links

Table of n, a(n) for n=1..26.

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

Formula

a(1)=12, a(2)=33, a(3)=133, a(4)=252, a(n) = 6*a(n-2) - a(n-4) + 46.

G.f.: x*(8*x^4+7*x^3-28*x^2-21*x-12) / ((x-1)*(x^2-2*x-1)*(x^2+2*x-1)). [Colin Barker, Dec 17 2012]

Example

a(5) = 6*133 - 12 + 46 = 832 and 832^2 + 855^2 = 1193^2 and 855-832=23 and gcd(832,855,1193)=1

Crossrefs

Cf. A117475.

Sequence in context: A032604 A043161 A043941 * A122436 A063554 A059805

Adjacent sequences: A117473 A117474 A117475 * A117477 A117478 A117479

Keyword

nonn,easy

Author

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

Status

approved