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%I #13 Sep 27 2020 13:38:46
%S 1,1,1,2,1,3,1,2,2,4,1,5,1,2,3,6,1,7,1,2,4,8,1,3,3,9,1,2,5,10,1,11,1,
%T 2,3,4,6,12,1,13,1,2,7,14,1,3,5,15,1,2,4,4,8,16,1,17,1,2,3,6,9,18,1,
%U 19,1,2,4,5,10,20,1,3,7,21
%N Array read by rows in which row n lists the divisors of n, but if n is a square then the square root of n appears twice.
%C Row n has length A161841(n). Row sums give A060866. - _Omar E. Pol_, Jan 06 2014
%H Omar E. Pol, <a href="http://www.polprimos.com">Determinacion geometrica de los numeros primos y perfectos</a>
%H Omar E. Pol, <a href="http://www.polprimos.com/imagenespub/polprdipi.jpg">Illustration: Divisors and pi(x)</a>
%e Array begins:
%e ....... 1,1;
%e ....... 1,2;
%e ....... 1,3;
%e ..... 1,2,2,4;
%e ....... 1,5;
%e ..... 1,2,3,6;
%e ....... 1,7;
%e ..... 1,2,4,8;
%e ..... 1,3,3,9;
%e ..... 1,2,5,10;
%e ....... 1,11;
%e ... 1,2,3,4,6,12;
%e ....... 1,13;
%e ..... 1,2,7,14;
%e ..... 1,3,5,15;
%e ... 1,2,4,4,8,16;
%t dsr[n_]:=If[IntegerQ[Sqrt[n]],Sort[Join[{Sqrt[n]},Divisors[n]]],Divisors[ n]]; Array[ dsr,30]//Flatten (* _Harvey P. Dale_, Sep 27 2020 *)
%Y Cf. A000005, A027750, A038548, A161841, A161842.
%K easy,nonn,tabf
%O 1,4
%A _Omar E. Pol_, Jun 23 2009
%E Keyword tabf added by _R. J. Mathar_, Jun 28 2009
%E Definition clarified by _Harvey P. Dale_, Sep 27 2020
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