A304207 a(1)=17; for n>1, a(n) = (a(n-1)^2 - 1)/2 if n is even, a(n-1) + 1 if n is odd.

17, 144, 145, 10512, 10513, 55261584, 55261585, 1526921388356112, 1526921388356113, 1165744463109679828308252234384, 1165744463109679828308252234385, 679480076635437837059150531810555804350472205781672488164112, 679480076635437837059150531810555804350472205781672488164113

Offset: 1

Author

Benjamin Knight, May 08 2018

Keywords

• nonn

Comments

{17, 144, 145}, {145, 10512, 10513}, {10513, 55261584, 55261585}, ... are sides {a < b < c} of the right triangles, with hypotenuse c = b + 1.

Links

• Eric Chen, Table of n, a(n) for n = 1..21

Crossrefs

Same basic form as A076601, A076602, A076603, and A076604.

Programs

Mathematica

nxt[{n_,a_}]:={n+1,If[OddQ[n],(a^2-1)/2,a+1]}; NestList[nxt,{1,17},20][[All,2]] (* Harvey P. Dale, Mar 27 2021 *)

PARI

a(n) = if(n==1,17,if(n%2,a(n-1)+1,(a(n-1)^2 - 1)/2)) \\ Eric Chen, Jun 09 2018