A076426 - OEIS

%I #6 Mar 30 2012 17:34:50

%S 5750,33866,74841,517250,577750,5538710,51414250,51454250,51687250,

%T 51727250,51748250,51858250,52525250,57515750,57535750,57575750,

%U 57757750,67597352,841794296,5120202250,5120802250,5121612250

%N Fixed points of the mapping k -> abs(reverse(lpd(k))-reverse(Lpf(k))). lpd(k) is the largest proper divisor and Lpf(k) is the largest prime factor of k.

%C Besides these fixed points (cycles of length 1) there are five cycles of length 2 ([9378, 9739], [518775, 522075], [5170250, 5197250], [5219475, 5249775], [5255750, 5755250]) and one cycle of length 3 ([7285, 7467, 9711]) below 8000000.

%F abs(reverse(lpd(n))-reverse(Lpf(n))) = n.

%e lpd(5750) = 2875; Lpf(5750) = 23; 5782 - 32 = 5750.

%o (PARI) {for(n=1,34000,v=divisors(n); a=matsize(v)[2]; z=if(a>1,v[a-1],1); p=0; while(z>0,d=divrem(z,10); z=d[1]; p=10*p+d[2]); z=if(n==1,1,vecmax(component(factor(n),1))); q=0; while(z>0,d=divrem(z,10); z=d[1]; q=10*q+d[2]); if(abs(p-q)==n,print1(n,",")))}

%Y Cf. A076423, A076425.

%K base,nonn

%O 1,1

%A _Klaus Brockhaus_, Oct 11 2002

%E Offset corrected and a(7)-a(22) from _Donovan Johnson_, Aug 09 2010