A304207 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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

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 *)

PROG

(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

CROSSREFS