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A269065 Irregular triangle read by rows: row n lists divisors of n-th composite number.

%I A269065 #20 Feb 16 2025 08:33:30
%S A269065 1,2,4,1,2,3,6,1,2,4,8,1,3,9,1,2,5,10,1,2,3,4,6,12,1,2,7,14,1,3,5,15,
%T A269065 1,2,4,8,16,1,2,3,6,9,18,1,2,4,5,10,20,1,3,7,21,1,2,11,22,1,2,3,4,6,8,
%U A269065 12,24,1,5,25,1,2,13,26,1,3,9,27,1,2,4,7,14,28,1,2,3,5,6,10,15,30,1,2,4,8,16,32,1,3,11,33,1,2,17,34
%N A269065 Irregular triangle read by rows: row n lists divisors of n-th composite number.
%C A269065 Subsequence of A027750.
%C A269065 Row sums give A073255.
%C A269065 Right border gives A002808.
%H A269065 Ilya Gutkovskiy, <a href="/A269065/a269065.pdf">Extended example</a>
%H A269065 Ilya Gutkovskiy, <a href="/A269065/a269065_1.pdf">Graphic additions</a>
%H A269065 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CompositeNumber.html">Composite Number</a>
%H A269065 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Divisor.html">Divisor</a>
%H A269065 <a href="/index/Di#divisors">Index entries for sequences related to divisors of numbers</a>
%e A269065 Triangle begins:
%e A269065 1,  2,  4;
%e A269065 1,  2,  3,  6;
%e A269065 1,  2,  4,  8;
%e A269065 1,  3,  9;
%e A269065 1,  2,  5,  10;
%e A269065 1,  2,  3,  4,  6,  12;
%e A269065 1,  2,  7,  14;
%e A269065 1,  3,  5,  15
%e A269065 1,  2,  4,  8,  16;
%e A269065 1,  2,  3,  6,  9,  18;
%e A269065 1,  2,  4,  5,  10, 20;
%e A269065 1,  3,  7,  21;
%e A269065 1,  2,  11, 22;
%e A269065 1,  2,  3,  4,  6,  8,  12, 24;
%e A269065 1,  5,  25;
%e A269065 1,  2,  13, 26;
%e A269065 1,  3,  9,  27;
%e A269065 1,  2,  4,  7,  14, 28;
%e A269065 1,  2,  3,  5,  6,  10, 15, 30;
%e A269065 1,  2,  4,  8,  16, 32;
%e A269065 1,  3,  11, 33;
%e A269065 1,  2,  17, 34;
%e A269065 ...
%t A269065 Flatten[Table[Divisors[Composite[n]], {n, 22}]]
%o A269065 (PARI) tabf(nn) =  forcomposite(c=1, nn, print(divisors(c), ", ")); \\ _Michel Marcus_, Feb 21 2016
%Y A269065 Cf. A002808, A027750, A035004 (row length), A133021, A133031, A138881.
%K A269065 nonn,tabf
%O A269065 1,2
%A A269065 _Ilya Gutkovskiy_, Feb 21 2016