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Number of seven-prime Carmichael numbers less than 10^n.
9

%I #21 Apr 20 2024 04:17:14

%S 0,0,0,0,0,0,0,0,0,0,2,41,262,1340,5359,19210,60150,172234,460553,

%T 1159167,2774702,6363475,14056367

%N Number of seven-prime Carmichael numbers less than 10^n.

%H Claude Goutier, <a href="http://www-labs.iro.umontreal.ca/~goutier/OEIS/A055553/">Text file readme.text summarizing enumeration of Carmichael numbers up to 10^22</a>.

%H Claude Goutier, <a href="/A055553/a055553.txt">Text file readme.text summarizing enumeration of Carmichael numbers up to 10^22</a>. [Local copy, with permission]

%H R. G. E. Pinch, <a href="http://s369624816.websitehome.co.uk/rgep/p82p.pdf">The Carmichael numbers up to 10^21</a>, Proceedings of Conference on Algorithmic Number Theory 2007.

%e The smallest Carmichael number with 7 prime factors is 5394826801 = 7*13*17*23*31*67*73, and there is one other 10-digit example, so a(10)=2.

%Y For k-prime Carmichael numbers up to 10^n for k = 3,4,...,11, see A132195, A174612, A174613, A174614, A174615, A174616, A174617, A299710, A299711.

%Y Cf. A002997, A006931, A055553.

%K nonn,more

%O 0,11

%A _Michel Lagneau_, Mar 23 2010

%E a(22) from _Claude Goutier_ added by _Amiram Eldar_, Apr 19 2024