A257574 Continued square root map applied to the sequence of positive even numbers, (2, 4, 6, 8, ...).

2, 1, 5, 8, 4, 7, 6, 8, 7, 2, 3, 1, 1, 0, 3, 9, 7, 6, 5, 6, 5, 5, 8, 5, 3, 4, 7, 9, 8, 0, 7, 0, 2, 5, 2, 4, 1, 6, 6, 9, 6, 9, 4, 4, 4, 0, 3, 5, 4, 2, 8, 6, 6, 7, 0, 3, 7, 5, 5, 0, 9, 6, 3, 4, 2, 1, 9, 4, 6, 2, 4, 0, 7, 4, 5, 4, 9, 7, 7, 1, 1, 8, 5, 9, 9, 8, 0

Offset: 1

Author

N. J. A. Sloane, May 02 2015

Keywords

• nonn
• cons

Comments

The continued square root or CSR map applied to a sequence b = (b(1), b(2), b(3), ...) is the number CSR(b) := sqrt(b(1)+sqrt(b(2)+sqrt(b(3)+sqrt(b(4)+...)))).

Taking out a factor sqrt(2), one gets CSR(2, 4, 6, 8, ...) = sqrt(2) CSR(1, 1, 3/8, 1/32, ...) < A002193*A001622 = (sqrt(5)+1)/sqrt(2). - M. F. Hasler, May 01 2018

Examples

			sqrt(2 + sqrt(4 + sqrt(6 + sqrt(8 + ...)))) = 2.1584768723110397656558534...
		

Links

• Hiroaki Yamanouchi, Table of n, a(n) for n = 1..400
• A. Herschfeld, On Infinite Radicals, Amer. Math. Monthly, 42 (1935), 419-429.
• Herman P. Robinson, The CSR Function, Popular Computing (Calabasas, CA), Vol. 4 (No. 35, Feb 1976), pages PC35-3 to PC35-4. Annotated and scanned copy.

Crossrefs

Cf. A072449, A257575..A257581, A105817, A099879, A001622, A105546.

Programs

PARI

(CSR(v,s)=forstep(i=#v,1,-1,s=sqrt(v[i]+s));s); t=0;for(N=5,oo,(t==t=Str(CSR([1..2*N]*2)))&&break;print(2*N": "t)) \\ Allows to see the convergence, which is reached when length of vector ~ precision [given as number of digits]. Using Str() to avoid infinite loop when internal representation is "fluctuating". - M. F. Hasler, May 04 2018

Extensions

a(27)-a(87) from Hiroaki Yamanouchi, May 03 2015

Edited by M. F. Hasler, May 01 2018