OFFSET
1,1
COMMENTS
Pythagoras's snail: begin the snail with an isosceles triangle (side = 1 unit). Then new triangle's right-angle sides are the previous hypotenuse and 1 unit length side.
From one term to the next one, the number added grows by 18, 19, 20 or 21 (tested up to 5000 terms).
To restate the comment immediately above: the second differences of the terms of the sequence consist of 18, 19, 20, or 21. - Harvey P. Dale, May 20 2019
FORMULA
a(n) = A072895(n) - 1. - Robert G. Wilson v, Feb 27 2013
EXAMPLE
17 triangles are needed to close the first turn. So there are 16 triangles in this turn. From the beginning, there are 53 triangles before closing the second turn... etc.
MATHEMATICA
w[n_] := ArcSin[ 1/Sqrt[n+1] ]//N; s[1] = w[1]; s[n_] := s[n] = s[n-1] + w[n]; a[n_] := (an = 1; While[ s[an] < 2*Pi*n, an++]; an-1); Table[ an = a[n]; Print[an]; an, {n, 1, 42}] (* Jean-François Alcover, Feb 24 2012 *)
PROG
(Python) from math import asin, sqrt, pi hyp=2 som=0 n=1 while n<500: if som+asin(1/sqrt(hyp))/pi*180>n*360: print hyp-2 n=n+1 som=som+asin(1/sqrt(hyp))/pi*180 hyp=hyp+1
CROSSREFS
KEYWORD
easy,nice,nonn
AUTHOR
Sébastien Dumortier, Apr 23 2008, Apr 25 2008
STATUS
approved