A066047 Numbers k that divide A001045(k-1).

5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 341, 347, 349, 353, 359

Offset: 1

Author

Benoit Cloitre, Dec 29 2001

Keywords

• nonn

Comments

The preponderance of entries are primes. The first which is not prime is 341.

All composite entries are 2-pseudoprimes. - Charles R Greathouse IV, Nov 04 2016

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A001045, A064739.

Programs

Maple

A066047 := proc(n)
    option remember ;
    if n = 1 then
        5 ;
    else
        for a from procname(n-1)+1 do
            if modp(A001045(a-1),a) =0 then
                return a;
            end if;
        end do:
    end if;
end proc:
seq(A066047(n),n=1..100) ; # R. J. Mathar, May 25 2023

Mathematica

a[0] = 0; a[1] = 1; a[n_] := a[n] = a[n - 1] + 2a[n - 2]; Select[ Range[500], IntegerQ[a[ # - 1]/# ] && # != 1 & ]

PARI

is(n)=Mod(2,3*n)^(n-1) == 1 \\ Charles R Greathouse IV, Nov 04 2016

Extensions

More terms from Robert G. Wilson v, Jan 03 2002