A192282 - OEIS

%I #12 Mar 30 2012 18:53:49

%S 1,8,17,120,717,729,957,8097,10785,12057,35817,44817,52863,58677,

%T 59757,76759,95397,102957,114117,119337,182157,206097,215997,230037,

%U 253977,263877,269277,271797,295377,321417,402657,435477,483117,485637,510837,586797,589317

%N Numbers n such that n and n+1 have same sum of anti-divisors.

%C Like A002961 but using anti-divisors.

%C Curiously 957 and 958 have same sum of divisors and same sum of anti-divisors.

%H Donovan Johnson, <a href="/A192282/b192282.txt">Table of n, a(n) for n = 1..1000</a>

%e Anti-divisors of 717 are 2, 5, 6, 7, 35, 41, 205, 287, 478 and their sum is 1066.

%e Anti-divisors of 718 are  3, 4, 5, 7, 35, 41, 205, 287, 479 and their sum is 1066.

%p with(numtheory);

%p P:=proc(n)

%p local a,b,i,k;

%p b:=2;

%p for i from 4 to n do

%p   a:=0;

%p   for k from 2 to i-1 do

%p     if abs((i mod k)- k/2) < 1 then a:=a+k; fi;

%p   od;

%p   if a=b then print(i-1); fi;

%p   b:=a;

%p od;

%p end:

%p P(200000);

%Y Cf. A002961, A066272, A192283.

%K nonn

%O 1,2

%A _Paolo P. Lava_, Jul 27 2011

%E Initial term a(1)=1 inserted, a(2)=9 through a(20)=119337 verified, and a(21)-a(28) added by _John W. Layman_, Aug 04 2011