OFFSET
1,4
COMMENTS
Definition of Pierce expansion: for a real number x (0<x<1), there is always a unique increasing positive integer sequence (a(i))_i>0 such that x = 1/a(1) - 1/a(1)/a(2) + 1/a(1)/a(2)/a(3) -1/a(1)/a(2)/a(3)/a(4) .. This expansion can be computed as follows: let u(0)=x and u(k+1) = u(k)/(u(k)-floor(u(k)); then a(n)=floor(u(n)). - Benoit Cloitre, Mar 14 2004
REFERENCES
P. Deheuvels, L'encadrement asymptotique des éléments de la série d'Engel d'un nombre réel, C. R. Acad. Sci. Paris, 295 (1982), 21-24.
F. Engel, Entwicklung der Zahlen nach Stammbruechen, Verhandlungen der 52. Versammlung deutscher Philologen und Schulmaenner in Marburg, 1913, pp. 190-191.
A. Renyi, A new approach to the theory of Engel's series, Ann. Univ. Sci. Budapest. Eotvos Sect. Math., 5 (1962), 25-32.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Simon Plouffe, Table of n, a(n) for n = 1..711
F. Engel, Entwicklung der Zahlen nach Stammbruechen, Verhandlungen der 52. Versammlung deutscher Philologen und Schulmaenner in Marburg, 1913, pp. 190-191. English translation by Georg Fischer, included with his permission.
P. Erdős and Jeffrey Shallit, New bounds on the length of finite Pierce and Engel series, Sem. Theor. Nombres Bordeaux (2) 3 (1991), no. 1, 43-53.
P. Liardet and P. Stambul, Séries d'Engel et fractions continuées, Journal de Théorie des Nombres de Bordeaux 12 (2000), 37-68.
Eric Weisstein's World of Mathematics, Engel Expansion
Eric Weisstein's World of Mathematics, Pi
FORMULA
Definition of Engel expansion: For a positive real number x (here Pi), define 1 <= a(1) <= a(2) <= a(3) <= ... so that x = 1/a(1) + 1/a(1)a(2) + 1/a(1)a(2)a(3) + ... by x(1)=x, a(n) = ceiling(1/x(n)), x(n+1) = x(n)a(n)-1. Expansion always exists and is unique. See references for more information.
EXAMPLE
1/1 + 1/1 + 1/1 + 1/8 + 1/(8*8) + 1/(8*8*17) <= Pi < 1/1 + 1/1 + 1/1 + 1/8 + 1/(8*8) + 1/(8*8*16), so a(6) = 17. - Peter Munn, Aug 14 2022
MAPLE
a(n):=proc(s)
local
i, j, max, aa, bb, lll, prod, S, T, kk;
S := evalf(abs(s));
max := 10^(Digits - 10);
prod := 1;
lll := [];
while prod <= max do
T := 1 + trunc(1/S);
S := frac(S*T);
lll := [op(lll), T];
prod := prod*T
end do;
RETURN(lll)
end: # Simon Plouffe, Apr 24 2016
MATHEMATICA
EngelExp[ A_, n_ ] := Join[ Array[ 1&, Floor[ A ]], First@Transpose@NestList[ {Ceiling[ 1/Expand[ #[[ 1 ]]#[[ 2 ]]-1 ]], Expand[ #[[ 1 ]]#[[ 2 ]]-1 ]}&, {Ceiling[ 1/(A-Floor[ A ]) ], A-Floor[ A ]}, n-1 ]]
EngelExp[ N[ Pi, 500000], 27]
CROSSREFS
KEYWORD
nonn,nice,easy
AUTHOR
EXTENSIONS
More terms from Olivier Gérard, Jul 10 2001
STATUS
approved