OFFSET
1,1
COMMENTS
Note that the indices here differ by one from those in WIFC (World Integer Factorization Center), N = int(pi*10^(n)), by Hisanori Mishima. Therefore to H. Mishima's index add one.
LINKS
Dario Alejandro Alpern, Java Applet: Factorization using the Elliptic Curve Method.
H. Mishima, Factorizations of many number sequences
H. Mishima, Factorizations of many number sequences
FORMULA
Numbers n such that A011545(n) is squarefree.
EXAMPLE
n=3: first 3 digits give 314=2*157
n=5: first 5 digits give 31415=5*61*103
n=8: 31415926=2*1901*8263
n=10: 3141592653=3*107*9786893
n=11: 31415926535=5*7*31*28954771
n=12: 314159265358=2*157079632679, etc.
MATHEMATICA
(* first do *) Needs["NumberTheory`NumberTheoryFunctions`"] (* then *) p = RealDigits[Pi, 10, 100][[1]]; fQ[n_] := Block[{fd = FromDigits@ Take[p, n]}, !PrimeQ@fd && SquareFreeQ@fd]; Select[Range@81, fQ@# &] (* Robert G. Wilson v *)
Module[{nn=120, p, c}, p=RealDigits[Pi, 10, nn][[1]]; Select[Range[nn], CompositeQ[ c=FromDigits[Take[p, #]]]&&SquareFreeQ[c]&]] (* Harvey P. Dale, Mar 25 2015 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Zak Seidov, Aug 19 2006
EXTENSIONS
More terms from Robert G. Wilson v, Aug 21 2006
STATUS
approved