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

1,2

Links

Table of n, a(n) for n=1..35.

Example

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

Prog

(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], ", "))}

Crossrefs

Cf. A074347, A076423.

Sequence in context: A256031 A073617 A034381 * A165301 A072440 A135522

Adjacent sequences: A076421 A076422 A076423 * A076425 A076426 A076427

Keyword

base,nonn

Author

Klaus Brockhaus, Oct 11 2002

Status

approved