A007547 - OEIS (original) (raw)

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

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).

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:

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