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A330355
Starting from n: as long as the decimal representation contains a positive multiple of 3, divide the largest and leftmost such substring by 3; a(n) corresponds to the final value.
1
0, 1, 2, 1, 4, 5, 2, 7, 8, 1, 10, 11, 4, 11, 14, 5, 4, 17, 2, 11, 20, 7, 22, 7, 8, 25, 22, 1, 28, 7, 10, 11, 4, 11, 14, 5, 4, 17, 2, 11, 40, 41, 14, 41, 44, 5, 14, 47, 4, 41, 50, 17, 52, 17, 2, 55, 52, 11, 58, 17, 20, 7, 22, 7, 8, 25, 22, 1, 28, 7, 70, 71, 8
OFFSET
0,3
COMMENTS
This sequence is a variant of A329424.
LINKS
FORMULA
a(n) <= n with equality iff n = 0 or n belongs to A325112.
a(3^k) = 1 for any k >= 0.
EXAMPLE
For n = 193:
- 193 gives 1 followed by 93/3 = 131,
- 131 gives 1 followed by 3/3 followed by 1 = 111,
- 111 gives 111/3 = 37,
- 37 gives 3/3 followed by 7 = 17,
- neither 1, 7 nor 17 are divisible by 3, so a(193) = 17.
MAPLE
f:= proc(n) option remember; local L, m, i, d, np1, j, s;
L:= convert(n, base, 10);
m:= nops(L);
for d from m to 1 by -1 do
for i from 1 to m-d+1 do
s:= convert(L[i..i+d-1], `+`);
if s > 0 and s mod 3 = 0 then
np1:= add(L[j]*10^(j-1), j=1..i-1)+1/3*add(L[j]*10^(j-1), j=i..i+d-1);
return procname(np1 + 10^(2+ilog10(np1)-(i+d))*add(L[j]*10^(j-1), j=i+d..m));
fi
od
od;
n
end proc:
map(f, [$0..100]); # Robert Israel, Dec 25 2019
PROG
(PARI) See Links section.
CROSSREFS
KEYWORD
nonn,base,look
AUTHOR
Rémy Sigrist, Dec 11 2019
STATUS
approved