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A208157 9-Knödel numbers.

%I A208157 #22 Feb 16 2025 08:33:16
%S A208157 21,27,45,63,99,105,117,153,171,189,207,261,273,279,333,369,387,423,
%T A208157 429,477,513,531,549,585,603,639,657,711,747,801,873,909,927,945,963,
%U A208157 981,1017,1143,1179,1197,1209,1233,1251,1341,1359,1365,1413,1467,1503,1557
%N A208157 9-Knödel numbers.
%H A208157 Amiram Eldar, <a href="/A208157/b208157.txt">Table of n, a(n) for n = 1..10000</a>
%H A208157 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/KnoedelNumbers.html">Knödel Numbers</a>
%p A208157 with(numtheory);
%p A208157 knodel:=proc(i,k)
%p A208157 local a,n,ok;
%p A208157 for n from k+1 to i do
%p A208157   ok:=1;
%p A208157   for a from 1 to n do
%p A208157      if gcd(a,n)=1 then  if (a^(n-k) mod n)<>1 then ok:=0; break; fi; fi;
%p A208157   od;
%p A208157   if ok=1 then print(n); fi;
%p A208157 od;
%p A208157 end:
%p A208157 knodel(10000,9)
%t A208157 Select[Range[12, 1560, 3], Divisible[# - 9, CarmichaelLambda[#]]&] (* _Jean-François Alcover_, Mar 01 2018 *)
%Y A208157 Cf. A002997, A050990, A033553, A050992, A050993, A208154-A208156, A208158.
%K A208157 nonn
%O A208157 1,1
%A A208157 _Paolo P. Lava_, Feb 24 2012