cp's OEIS Frontend

A161904 Array read by rows in which row n list the divisors of n, but if n is a square then the square root of n appears repeated. Also, the divisors appear as pairs (a,b), where a <= b, such that a*b = n.

%I A161904 #12 Dec 23 2015 02:35:03
%S A161904 1,1,1,2,1,3,1,4,2,2,1,5,1,6,2,3,1,7,1,8,2,4,1,9,3,3,1,10,2,5,1,11,1,
%T A161904 12,2,6,3,4,1,13,1,14,2,7,1,15,3,5,1,16,2,8,4,4,1,17,1,18,2,9,3,6,1,
%U A161904 19,1,20,2,10,4,5,1,21,3,7
%N A161904 Array read by rows in which row n list the divisors of n, but if n is a square then the square root of n appears repeated. Also, the divisors appear as pairs (a,b), where a <= b, such that a*b = n.
%C A161904 Row lengths are 2*A038548(n). - _R. J. Mathar_ Jun 28 2009
%e A161904 Array begins:
%e A161904 (1,1);
%e A161904 (1,2);
%e A161904 (1,3);
%e A161904 (1,4),(2,2);
%e A161904 (1,5);
%e A161904 (1,6),(2,3);
%e A161904 (1,7);
%e A161904 (1,8),(2,4);
%e A161904 (1,9),(3,3);
%e A161904 (1,10),(2,5);
%e A161904 (1,11);
%e A161904 (1,12),(2,6),(3,4);
%e A161904 (1,13);
%e A161904 (1,14),(2,7);
%e A161904 (1,15),(3,5);
%e A161904 (1,16),(2,8),(4,4);
%Y A161904 See also A161901 for another version.
%Y A161904 Cf. A000005, A027750, A038548, A161841.
%K A161904 easy,nonn,tabf
%O A161904 1,4
%A A161904 _Omar E. Pol_, Jun 23 2009
%E A161904 Keyword tabf added by _R. J. Mathar_, Jun 28 2009