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A304254 Irregular triangle read by rows: row n lists divisors of n^2 in decreasing order.

%I A304254 #22 May 02 2025 03:31:31
%S A304254 1,4,2,1,9,3,1,16,8,4,2,1,25,5,1,36,18,12,9,6,4,3,2,1,49,7,1,64,32,16,
%T A304254 8,4,2,1,81,27,9,3,1,100,50,25,20,10,5,4,2,1,121,11,1,144,72,48,36,24,
%U A304254 18,16,12,9,8,6,4,3,2,1,169,13,1,196,98,49,28,14,7,4,2,1
%N A304254 Irregular triangle read by rows: row n lists divisors of n^2 in decreasing order.
%H A304254 Amiram Eldar, <a href="/A304254/b304254.txt">Table of n, a(n) for n = 1..11958</a> (rows 1..600 flattened)
%e A304254 Triangle begins:
%e A304254   1;
%e A304254   4, 2, 1;
%e A304254   9, 3, 1;
%e A304254   16, 8, 4, 2, 1;
%e A304254   25, 5, 1;
%e A304254   36, 18, 12, 9, 6, 4, 3, 2, 1;
%e A304254   49, 7, 1;
%e A304254   64, 32, 16, 8, 4, 2, 1;
%e A304254   81, 27, 9, 3, 1;
%e A304254   100, 50, 25, 20, 10, 5, 4, 2, 1;
%e A304254   121, 11, 1;
%e A304254   144, 72, 48, 36, 24, 18, 16, 12, 9, 8, 6, 4, 3, 2, 1;
%e A304254   169, 13, 1;
%e A304254   196, 98, 49, 28, 14, 7, 4, 2, 1;
%e A304254   225, 75, 45, 25, 15, 9, 5, 3, 1;
%e A304254   256, 128, 64, 32, 16, 8, 4, 2, 1;
%e A304254   289, 17, 1;
%e A304254   324, 162, 108, 81, 54, 36, 27, 18, 12, 9, 6, 4, 3, 2, 1;
%e A304254   361, 19, 1;
%e A304254   400, 200, 100, 80, 50, 40, 25, 20, 16, 10, 8, 5, 4, 2, 1;
%t A304254 Table[Reverse[Divisors[n^2]], {n, 1, 14}] // Flatten (* _Amiram Eldar_, May 02 2025 *)
%o A304254 (PARI) row(n) = Vecrev(divisors(n^2)); \\ _Amiram Eldar_, May 02 2025
%Y A304254 Cf. A048691 (row lengths), A065764 (row sums), A056538.
%K A304254 nonn,tabf
%O A304254 1,2
%A A304254 _Kritsada Moomuang_, May 09 2018