# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/

Search: id:a225511
Showing 1-1 of 1

%I A225511 #13 Mar 28 2019 07:02:12
%S A225511 33,65,245,345,1353,1421,1505,2405,3185,4433,4745,6293,6923,7733,8729,
%T A225511 9065,9443,9785,15113,16113,18473,19565,21593,30485,30705,32513,35705,
%U A225511 42833,45353,50141,55685,57017,64505,66521,67065,73073,79553,80093,83657,91553,96473
%N A225511 -7-Knödel numbers.
%C A225511 Extension of k-Knodel numbers to k negative, in this case equal to -7. Composite numbers n > 0 such that if 1 < a < n and gcd(n,a) = 1 then a^(n+7) = 1 mod n.
%H A225511 Amiram Eldar, <a href="/A225511/b225511.txt">Table of n, a(n) for n = 1..1000</a>
%H A225511 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/KnoedelNumbers.html">Knödel Numbers</a>
%p A225511 with(numtheory); ListA225511:=proc(q,k) local a,n,ok;
%p A225511 for n from 2 to q do if not isprime(n) then ok:=1; for a from 1 to n do
%p A225511 if gcd(a,n)=1 then if (a^(n-k)-1) mod n<>0 then ok:=0; break; fi; fi;
%p A225511 od; if ok=1 then print(n); fi; fi; od; end: ListA225511(10^6,-7);
%t A225511 Select[Range[10000], CompositeQ[#] && Divisible[# + 7, CarmichaelLambda[#]] &] (* _Amiram Eldar_, Mar 28 2019 *)
%Y A225511 Cf. A208728.
%Y A225511 Cf. A225506, A225507, A225508, A225509, A225510, A225512, A225513, A225514.
%K A225511 nonn
%O A225511 1,1
%A A225511 _Paolo P. Lava_, May 09 2013
%E A225511 More terms from _Amiram Eldar_, Mar 28 2019

# Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE