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

%I A066047 #20 May 25 2023 12:46:21
%S A066047 5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,
%T A066047 101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,
%U A066047 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
%N A066047 Numbers k that divide A001045(k-1).
%C A066047 The preponderance of entries are primes. The first which is not prime is 341.
%C A066047 All composite entries are 2-pseudoprimes. - _Charles R Greathouse IV_, Nov 04 2016
%H A066047 Vincenzo Librandi, <a href="/A066047/b066047.txt">Table of n, a(n) for n = 1..1000</a>
%p A066047 A066047 := proc(n)
%p A066047     option remember ;
%p A066047     if n = 1 then
%p A066047         5 ;
%p A066047     else
%p A066047         for a from procname(n-1)+1 do
%p A066047             if modp(A001045(a-1),a) =0 then
%p A066047                 return a;
%p A066047             end if;
%p A066047         end do:
%p A066047     end if;
%p A066047 end proc:
%p A066047 seq(A066047(n),n=1..100) ; # _R. J. Mathar_, May 25 2023
%t A066047 a[0] = 0; a[1] = 1; a[n_] := a[n] = a[n - 1] + 2a[n - 2]; Select[ Range[500], IntegerQ[a[ # - 1]/# ] && # != 1 & ]
%o A066047 (PARI) is(n)=Mod(2,3*n)^(n-1) == 1 \\ _Charles R Greathouse IV_, Nov 04 2016
%Y A066047 Cf. A001045, A064739.
%K A066047 nonn
%O A066047 1,1
%A A066047 _Benoit Cloitre_, Dec 29 2001
%E A066047 More terms from _Robert G. Wilson v_, Jan 03 2002