A133564 - OEIS

A133564

a(1)=1. a(n+1) = sum{k=isolated divisors of n} a(k). An isolated divisor, k, of n is a positive divisor of n where neither (k-1) nor (k+1) divides n.

%I #8 Apr 09 2014 10:16:01

%S 1,1,0,1,1,2,2,3,4,5,6,7,9,10,12,14,18,19,25,26,31,34,40,41,53,55,64,

%T 69,82,83,100,101,119,126,144,148,180,181,206,216,250,251,292,293,334,

%U 352,392,393,460,463,522,541,606,607,696,704,784,810,892,893,1026,1027,1127

%N a(1)=1. a(n+1) = sum{k=isolated divisors of n} a(k). An isolated divisor, k, of n is a positive divisor of n where neither (k-1) nor (k+1) divides n.

%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 isolated divisors of 20 are 10 and 20. Therefore a(21) = a(10) + a(20) = 5 + 26 = 31.

%Y Cf. A133565.

%K nonn

%O 1,6

%A _Leroy Quet_, Sep 16 2007

%E Extended by _Ray Chandler_, Jun 25 2008