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A340595 a(n) is the least k for which A340594(k) = n. 2
2, 4, 8, 21, 42, 65, 80, 217, 488, 721, 2120, 2349, 2796, 9214, 16043, 23287, 28626, 43588, 58176, 116982, 213435, 444329, 640673, 967248, 1399895, 1449156, 1528785, 2768054, 2915135, 3631071, 3673118, 5032731, 12977420 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,1
COMMENTS
a(n) is the least k >= 2 from which it takes exactly n iterations of A340592 to reach 0, 1 or a prime.
LINKS
EXAMPLE
Starting from 21, it takes 3 iterations of A340592 to reach 0,1 or a prime: 21 -> 16 -> 14 -> 13. Since this is the first case where 3 iterations are required, a(3) = 21.
MAPLE
dcat:= proc(L) local i, x;
x:= L[-1];
for i from nops(L)-1 to 1 by -1 do
x:= 10^(1+ilog10(x))*L[i]+x
od;
x
end proc:
f:= proc(n) local F;
F:= sort(ifactors(n)[2], (a, b) -> a[1] < b[1]);
dcat(map(t -> t[1]$t[2], F)) mod n;
end proc:
g:= proc(n) option remember;
if isprime(n) then 0 else 1 + procname(f(n)) fi
end proc:
g(0):= 0: g(1):= 0:
V:= Array(0..30): count:= 0:
for n from 2 while count < 31 do
v:= f(n);
if v::integer and v <= 100 and V[v] = 0 then
count:= count+1; V[v]:= n;
fi
od:
convert(V, list);
CROSSREFS
Sequence in context: A309868 A059731 A001315 * A216643 A002040 A162110
KEYWORD
nonn
AUTHOR
J. M. Bergot and Robert Israel, Jan 13 2021
STATUS
approved

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Last modified February 25 02:17 EST 2024. Contains 370308 sequences. (Running on oeis4.)