A076425 Numbers n such that zero is never reached by iterating the mapping k -> abs(reverse(lpd(k))-reverse(gpf(k))). lpd(k) is the largest proper divisor and gpf(k) is the largest prime factor of k.

2074, 2113, 2179, 2914, 3111, 4112, 4371, 4390, 4456, 4956, 4978, 5185, 5450, 5750, 6474, 6585, 6827, 7248, 7259, 7285, 7467, 8175, 8625, 8647, 9378, 9711, 9739, 10199, 10975, 11407, 11752, 12006, 12232, 12338, 12445, 12826, 13224, 13396

Offset

1,1

Comments

n such that A076423(n) = -1.

Links

Table of n, a(n) for n=1..38.

Example

For 4112 the mapping leads to a fixed point (cf. A076426): 4112 -> 5750 -> 5750 -> ...; for 2074 the mapping leads to a cycle: 2074 -> 7285 -> 7467 -> 9711 -> 7285 -> ...

Prog

(PARI) {stop=20; for(n=1, 13600, c=1; b=1; k=n; while(b&&c<stop, v=divisors(k); 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(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, print1(n, ", ")))}

Crossrefs

Cf. A076423, A076426.

Sequence in context: A221052 A062913 A096927 * A249654 A180921 A270537

Adjacent sequences: A076422 A076423 A076424 * A076426 A076427 A076428

Keyword

base,nonn

Author

Klaus Brockhaus, Oct 11 2002

Status

approved