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 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
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS 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

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Last modified May 18 23:41 EDT 2021. Contains 344009 sequences. (Running on oeis4.)