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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. 2
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 20 02:35 EDT 2019. Contains 328244 sequences. (Running on oeis4.)