A076603 a(1)=9, a(n_even)=(a(n-1)^2-1)/2; a(n_odd)=a(n-1)+1.

9, 40, 41, 840, 841, 353640, 353641, 62530978440, 62530978441, 1955061632394403395240, 1955061632394403395241, 1911132993230334657643987512400814230724040, 1911132993230334657643987512400814230724041

Offset

1,1

Comments

{9, 40, 41}, {41, 840, 841}, {841, 353640, 353641}... are sides {a<b<c} of the right triangles, with hypotenuse c=b+1.

Links

Table of n, a(n) for n=1..13.

Mathematica

nxt[{n_, a_}]:={n+1, If[EvenQ[n+1], (a^2-1)/2, a+1]}; Transpose[ NestList[ nxt, {1, 9}, 10]][[2]] (* Harvey P. Dale, Oct 15 2012 *)

Crossrefs

Sequence in context: A173764 A331343 A002085 * A346336 A003354 A063164

Adjacent sequences: A076600 A076601 A076602 * A076604 A076605 A076606

Keyword

easy,nonn

Author

Zak Seidov, Oct 21 2002

Extensions

More terms from Harvey P. Dale, Oct 15 2012

Status

approved