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A029554 Quasi-Carmichael numbers to base 9: squarefree composites n such that (n,2*3*5*7) = 1 and prime p|n ==> p-9|n-9. 2

%I

%S 209,6409,9361,11713,12749,19721,21593,32509,50609,74269,85289,88559,

%T 91793,99199,100529,152329,167977,187889,235049,271469,313049,471977,

%U 742729,828529,841033,925129,1057793,1078649,1186949,1265609,1324609

%N Quasi-Carmichael numbers to base 9: squarefree composites n such that (n,2*3*5*7) = 1 and prime p|n ==> p-9|n-9.

%C If multiples of 2, 3, 5 and 7 are not excluded, then terms like 21, 33, 65, 77, 105, 165, 231,... belong to the sequence. - _Giovanni Resta_, May 21 2013

%H Giovanni Resta, <a href="/A029554/b029554.txt">Table of n, a(n) for n = 1..2091</a> (terms < 10^12)

%H <a href="/index/Ca#Carmichael">Index entries for sequences related to Carmichael numbers.</a>

%t qcm[n_, d_] := Block[{p, e}, {p, e} = Transpose@FactorInteger@n; Length[p] > 1 && Max[e] == 1 && d < Min[p] && And @@ IntegerQ /@ ((n - d)/(p - d))]; Select[Range[10^6], qcm[#, 9] &] (* _Giovanni Resta_, May 21 2013 *)

%K nonn

%O 1,1

%A _David W. Wilson_

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Last modified March 29 05:39 EDT 2020. Contains 333105 sequences. (Running on oeis4.)