OFFSET
1,1
REFERENCES
D. Olivastro, Ancient Puzzles. Bantam Books, NY, 1993, p. 21.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Bert Dobbelaere, Table of n, a(n) for n = 1..1000
J. H. Conway, FRACTRAN: a simple universal programming language for arithmetic, in T. M. Cover and Gopinath, eds., Open Problems in Communication and Computation, Springer, NY 1987, pp. 4-26.
R. K. Guy, Conway's prime producing machine, Math. Mag. 56 (1983), no. 1, 26-33.
MAPLE
a:= proc(n) option remember; local l, p, m, k;
l:= [17/91, 78/85, 19/51, 23/38, 29/33, 77/29, 95/23,
77/19, 1/17, 11/13, 13/11, 15/2, 1/7, 55/1]:
if n=1 then b(0):= 2; a(0):= 0 else a(n-1) fi;
p:= b(n-1);
for m do for k while not type(p*l[k], integer) do od;
p:= p*l[k];
if 2^ilog2(p)=p then break fi
od:
b(n):= p;
m + a(n-1)
end:
seq(a(n), n=1..10); # Alois P. Heinz, May 01 2011
MATHEMATICA
Clear[a]; a[n_] := a[n] = Module[{l, p, m, k}, l = {17/91, 78/85, 19/51, 23/38, 29/33, 77/29, 95/23, 77/19, 1/17, 11/13, 13/11, 15/2, 1/7, 55/1}; If[n == 1, b[0] = 2; a[0] = 0, a[n-1]]; p = b[n-1]; For[m=1, True, m++, For[k=1, !IntegerQ[p*l[[k]]], k++]; p = p*l[[k]]; If[2^(Length[IntegerDigits[p, 2]]-1) == p, Break[]]]; b[n] = p; m + a[n-1]]; Table[Print[a[n]]; a[n], {n, 1, 30}] (* Jean-François Alcover, Nov 25 2014, after Alois P. Heinz *)
PROG
(Haskell)
import Data.List (elemIndices)
a007547 n = a007547_list !! n
a007547_list = tail $ elemIndices 2 $ map a006530 a007542_list
-- Reinhard Zumkeller, Jan 24 2012
CROSSREFS
KEYWORD
easy,nonn,nice
AUTHOR
EXTENSIONS
More terms from Alois P. Heinz, May 01 2011
STATUS
approved