A076424 Smallest number that requires n steps to reach 0 when iterating 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.

1, 2, 3, 12, 31, 23, 56, 102, 193, 257, 570, 1129, 4970, 3229, 11551, 11969, 24232, 20094, 24103, 35996, 100090, 222284, 116269, 231488, 388768, 1751753, 2046872, 1140163, 1149979, 2156214, 3199384, 2971734, 7018074, 10163234, 13135933

Offset: 1

Author

Klaus Brockhaus, Oct 11 2002

Keywords

• base
• nonn

Examples

			a(5) =31 since 31 requires 5 steps, but no m < 31 does. Although 23 < 31, 23 requires 6 steps.
		

Crossrefs

Cf. A074347, A076423.

Programs

PARI

{m=36; z=19200000; v=listcreate(m); for(i=1,m,listinsert(v,-1,i)); for(n=1,z,c=1; b=1; k=n; while(b&&c<=m, d=divisors(k); i=matsize(d)[2]-1; z=if(i>0,d[i],1); p=0; while(z>0,d=divrem(z,10); z=d[1]; p=10*p+d[2]); z= if(k==1,1,vecmax(component(factor(k),1))); q=0; while(z>0,d=divrem(z,10); z=d[1]; q=10*q+d[2]); a= abs(p-q); if(a==0,b=0,k=a; c++)); if(a==0,if(v[c]<0,v[c]=n; print1([c,n])))); print(); for(i=1,m,print1(v[i],","))}