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A269065 Irregular triangle read by rows: row n lists divisors of n-th composite number. 1

%I

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

%C Subsequence of A027750.

%C Row sums give A073255.

%C Right border gives A002808.

%H Ilya Gutkovskiy, <a href="/A269065/a269065.pdf">Extended example</a>

%H Ilya Gutkovskiy, <a href="/A269065/a269065_1.pdf">Graphic additions</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/CompositeNumber.html">Composite Number</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Divisor.html">Divisor</a>

%H <a href="/index/Di#divisors">Index entries for sequences related to divisors of numbers</a>

%e Triangle begins:

%e 1, 2, 4;

%e 1, 2, 3, 6;

%e 1, 2, 4, 8;

%e 1, 3, 9;

%e 1, 2, 5, 10;

%e 1, 2, 3, 4, 6, 12;

%e 1, 2, 7, 14;

%e 1, 3, 5, 15

%e 1, 2, 4, 8, 16;

%e 1, 2, 3, 6, 9, 18;

%e 1, 2, 4, 5, 10, 20;

%e 1, 3, 7, 21;

%e 1, 2, 11, 22;

%e 1, 2, 3, 4, 6, 8, 12, 24;

%e 1, 5, 25;

%e 1, 2, 13, 26;

%e 1, 3, 9, 27;

%e 1, 2, 4, 7, 14, 28;

%e 1, 2, 3, 5, 6, 10, 15, 30;

%e 1, 2, 4, 8, 16, 32;

%e 1, 3, 11, 33;

%e 1, 2, 17, 34;

%e ...

%t Flatten[Table[Divisors[Composite[n]], {n, 22}]]

%o (PARI) tabf(nn) = forcomposite(c=1, nn, print(divisors(c), ", ")); \\ _Michel Marcus_, Feb 21 2016

%Y Cf. A002808, A027750, A035004 (row length), A133021, A133031, A138881.

%K nonn,tabf

%O 1,2

%A _Ilya Gutkovskiy_, Feb 21 2016

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Last modified April 16 17:01 EDT 2021. Contains 343050 sequences. (Running on oeis4.)