

A068192


Let a(1)=2, f(n) = 4*a(1)*a(2)*...*a(n1) for n >= 1 and a(n) = f(n)prevprime(f(n)1) for n >= 2, where prevprime(x) is the largest prime < x.


4



2, 3, 5, 7, 11, 13, 17, 19, 31, 29, 23, 41, 43, 37, 89, 59, 53, 67, 79, 71, 137, 109, 239, 167, 199, 47, 83, 97, 61, 373, 101, 179, 193, 131, 151, 73, 263, 593, 139, 113, 157, 103, 241, 181, 397, 233, 617, 311, 191, 229, 271, 269, 127, 223, 331, 337, 211, 163
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OFFSET

1,1


COMMENTS

The terms are easily seen to be distinct. It is conjectured that every element is prime. Do all primes occur in the sequence?
First 1000 terms are primes.  Mauro Fiorentini, Aug 01 2020


LINKS

Mauro Fiorentini, Table of n, a(n) for n = 1..1000


MATHEMATICA

<<NumberTheory`PrimeQ` (* Load ProvablePrimeQ function, needed below. *)
f[1]=4; f[n_] := f[n]=f[n1]a[n1]; a[n_] := a[n]=Module[{i}, For[i=2, True, i++, If[ProvablePrimeQ[f[n]i], Return[i]]]]


PROG

(MuPAD) f := 4:for n from 1 to 50 do a := fnumlib::prevprime(f2):f := f*a:print(a) end_for


CROSSREFS

Cf. A068193 has the indices of the primes in this sequence. A066631 has the sequence of f's. Also see A067836.
Sequence in context: A177000 A117843 A293667 * A225083 A002200 A181561
Adjacent sequences: A068189 A068190 A068191 * A068193 A068194 A068195


KEYWORD

nonn,changed


AUTHOR

Frank Buss (fb(AT)frankbuss.de), Feb 19 2002


EXTENSIONS

Edited by Dean Hickerson, Jun 10 2002


STATUS

approved



