A007547 Number of steps to compute n-th prime in PRIMEGAME (slow version). (Formerly M5075)

19, 69, 281, 710, 2375, 3893, 8102, 11361, 19268, 36981, 45680, 75417, 101354, 118093, 152344, 215797, 293897, 327571, 429229, 508284, 556494, 701008, 809381, 990746, 1274952, 1435957, 1531854, 1712701, 1820085, 2021938, 2835628, 3107393, 3549288, 3723821

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

Table of n, a(n) for n=1..34.

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

Cf. A007542, A007546.

Cf. A006530, A034785.

Sequence in context: A300463 A204675 A007546 * A217081 A010007 A172078

Adjacent sequences: A007544 A007545 A007546 * A007548 A007549 A007550

Keyword

easy,nonn,nice

Author

N. J. A. Sloane

Extensions

More terms from Alois P. Heinz, May 01 2011

Status

approved