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%I #20 May 12 2024 11:17:04
%S 1,1,1,1,1,3,1,1,1,1,5,1,1,4,1,1,7,1,5,1,1,1,9,1,1,5,1,7,1,11,1,1,1,1,
%T 13,1,1,4,1,1,6,10,15,1,1,1,11,1,17,1,1,9,1,1,19,1,13,1,1,1,7,21,1,1,
%U 1,9,1,23,1,1,16,1,1,25,1,17,1,13,1,1,27,1,11,1,8,1,19,1,29,1,1,1,1,31,1,1,1,5,13
%N Irregular triangle read by rows in which row n >= 2 lists the divisors d of n such that d^n mod n = d.
%e Triangle begins:
%e 1;
%e 1;
%e 1;
%e 1;
%e 1, 3;
%e 1;
%e 1;
%e 1;
%e 1, 5;
%e 1;
%e 1, 4;
%e 1;
%e 1, 7;
%e 1, 5;
%e 1;
%e 1;
%e 1, 9;
%e 1;
%e 1, 5;
%e 1, 7;
%e 1, 11;
%e 1;
%e 1;
%e 1;
%e 1, 13;
%e 1;
%e 1, 4;
%e 1;
%e 1, 6, 10, 15;
%e ...
%t row[n_] := Select[Divisors[n], PowerMod[#, n, n] == # &]; Array[row, 64, 2] // Flatten (* _Amiram Eldar_, Apr 11 2024 *)
%o (Magma) [[d: d in Divisors(n) | d^n mod n eq d]: n in [2..65]];
%Y Cf. A027750, A182816, A279024, A371513, A371883.
%K nonn,tabf
%O 2,6
%A _Juri-Stepan Gerasimov_, Apr 10 2024