A161904 - OEIS

%I #12 Dec 23 2015 02:35:03

%S 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 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 19,1,20,2,10,4,5,1,21,3,7

%N 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 Row lengths are 2*A038548(n). - _R. J. Mathar_ Jun 28 2009

%e Array begins:

%e (1,1);

%e (1,2);

%e (1,3);

%e (1,4),(2,2);

%e (1,5);

%e (1,6),(2,3);

%e (1,7);

%e (1,8),(2,4);

%e (1,9),(3,3);

%e (1,10),(2,5);

%e (1,11);

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

%e (1,13);

%e (1,14),(2,7);

%e (1,15),(3,5);

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

%Y See also A161901 for another version.

%Y Cf. A000005, A027750, A038548, A161841.

%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