Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #19 Nov 23 2021 18:11:22
%S 0,1,1,3,1,5,1,7,2,9,1,11,1,13,7,15,1,17,1,19,1,21,1,23,2,25,13,27,1,
%T 29,1,31,2,33,17,35,1,37,19,39,1,41,1,43,1,45,1,47,1,49,5,51,1,53,3,
%U 55,2,57,1,59,1,61,31,63,4,65,1,67,17,69,1,71,1,73,37,75,19,77,1,79,1,81,1,83,1,85,43,87,1,89
%N a(n) = (n-1) / A346467(n).
%C Numbers n such that a(n) = 1 are A248614(m)+1 for m > 0. These are all primes together with A317210. The set of these numbers has zero asymptotic density.
%H Antti Karttunen, <a href="/A346468/b346468.txt">Table of n, a(n) for n = 1..20000</a>
%F a(n) = (n-1) / A346467(n).
%F a(n) = (n-1) / A002322(A027642(n-1)).
%t {0}~Join~Array[#/CarmichaelLambda@ Denominator@ BernoulliB@ # &, 89] (* _Michael De Vlieger_, Nov 23 2021 *)
%o (PARI) A346468(n) = if(1==n,0,my(m=1); fordiv(n-1,d,if(isprime(1+d),m = lcm(m,d))); ((n-1)/m));
%Y Cf. A002322, A027642, A248614, A317210, A346467.
%K nonn
%O 1,4
%A _Antti Karttunen_ and _Thomas Ordowski_, Jul 22 2021