A133780 - OEIS

%I #9 Mar 11 2014 01:32:22

%S 1,2,1,2,1,2,3,1,2,1,2,1,2,3,4,1,2,1,2,1,2,3,1,2,4,5,1,2,1,2,3,4,1,2,

%T 1,2,1,2,3,5,6,1,2,1,2,1,2,3,4,1,2,1,2,4,5,1,2,3,6,7,1,2,1,2,1,2,3,4,

%U 1,2,1,2,1,2,3,1,2,7,8,1,2,1,2,3,4,5,6,1,2,1,2,1,2,3,1,2,1,2,1,2,3,4,8,9,1

%N Irregular array: n-th row lists the "non-isolated divisors" of (2n). A positive divisor, k, of n is non-isolated if (k-1) or (k+1) also divides n.

%C No odd integer has any non-isolated divisors. The number of terms in the n-th row of the array is A132747(2n).

%e The positive divisors of 20 are 1,2,4,5,10,20. Of these, 1 and 2 are adjacent and 4 and 5 are adjacent. So the non-isolated divisors of 20 are 1,2,4,5.

%Y Cf. A133779, A132747, A132748.

%K nonn,tabf

%O 1,2

%A _Leroy Quet_, Sep 23 2007

%E Extended by _Ray Chandler_, Jun 24 2008