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a(n) is the smallest k with n prime factors such that 2^(k-1) == 1 (mod k) and p-1 does not divide k-1 for every prime p dividing k.
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%I #21 Jun 09 2020 03:36:56

%S 7957,617093,134564501,384266404601,8748670222601,6105991025919737,

%T 901196605940857381

%N a(n) is the smallest k with n prime factors such that 2^(k-1) == 1 (mod k) and p-1 does not divide k-1 for every prime p dividing k.

%C Conjecture: a(n) > A006931(n) for every n > 2.

%C a(6)-a(8) derived from Feitsma's tables of pseudoprimes. a(9) > 2^64. - _Giovanni Resta_, Jul 19 2018

%C From _Daniel Suteu_, Jun 08 2020: (Start)

%C a(9) <= 521957994426556057126261,

%C a(10) <= 1315856103949347820015303981,

%C a(11) <= 6357507186189933506573017225316941,

%C a(12) <= 77822245466150976053960303855104674781. (End)

%H Jan Feitsma and William Galway, <a href="http://www.cecm.sfu.ca/Pseudoprimes/index-2-to-64.html">Tables of pseudoprimes and related data</a>

%Y Cf. A001567, A121707, A316907.

%K nonn,more

%O 2,1

%A _Thomas Ordowski_, Jul 16 2018

%E More terms from _Michel Marcus_, Jul 16 2018

%E a(6)-a(8) from _Giovanni Resta_, Jul 19 2018