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%I #17 Dec 03 2021 12:47:30
%S 21,45,49,81,85,91,93,111,117,121,133,141,145,165,175,177,201,205,209,
%T 213,217,221,231,235,247,253,261,265,273,289,291,301,309,319,325,333,
%U 357,361,365,369,381,391,411,415,441,445,451,453,465,469,477,481,493
%N Composite numbers k+1 such that A002322(A027760(k)) = k.
%C Also, composite numbers n such that LCM( p-1 : prime p|A027642(n-1) ) = n-1. Also, composite numbers n such that LCM( p-1 : p is prime & (p-1)|(n-1) ) = n-1. - _Max Alekseyev_, Dec 03 2021
%C Contains all Carmichael numbers except 2628073, 3224065, 23382529, 182356993, 1419339691, ...
%H Amiram Eldar, <a href="/A317210/b317210.txt">Table of n, a(n) for n = 1..10000</a>
%t 1 + Select[Range[500], CompositeQ[# + 1] && CarmichaelLambda[ Times @@ Select[1 + Divisors@ #, PrimeQ]] == # &] (* _Giovanni Resta_, Aug 13 2018 *)
%o (PARI) a027760(n) = denominator(sumdiv(n, d, if(isprime(d+1), 1/(d+1))));
%o a002322(n) = lcm(znstar(n)[2]);
%o isok(n) = !isprime(n) && (n--) && !frac(a002322(a027760(n))/n); \\ _Michel Marcus_, Aug 13 2018
%Y Cf. A027760, A002322.
%K nonn
%O 1,1
%A _Max Alekseyev_ and _Thomas Ordowski_, Jul 09 2018
%E More terms from _Giovanni Resta_, Aug 13 2018
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