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A221697
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Numbers whose largest digit of all divisors is 2.
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3
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2, 22, 121, 202, 211, 1021, 1201, 2011, 2111, 2221, 2222, 10201, 10211, 12011, 12101, 12211, 12221, 20011, 20021, 20101, 20201, 20222, 21001, 21011, 21101, 21121, 21211, 21221, 22111, 22121, 101021, 101221, 102001, 102101, 102121, 110221, 111121, 111211, 111221, 112111, 112121
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OFFSET
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1,1
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COMMENTS
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Also numbers k such that the largest digit of the concatenation of all the divisors (A037278) of k is 2.
Numbers k such that A209928(k) = 2.
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LINKS
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EXAMPLE
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10201 is a term because the largest digit of all the divisors of 10201 (1, 101, 10201) is 2.
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MAPLE
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isA221697 := proc(n)
local dgs, d;
dgs := {} ;
for d in numtheory[divisors](n) do
dgs := dgs union convert(convert(d, base, 10), set) ;
end do:
if max(op(dgs)) = 2 then
true;
else
false;
end if;
end proc:
for n from 2 to 112121 do
if isA221697(n) then
printf("%d, ", n) ;
end if;
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MATHEMATICA
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Select[Range[115000], Max[Flatten[IntegerDigits/@Divisors[#]]]==2&] (* Harvey P. Dale, Dec 15 2014 *)
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PROG
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(Python)
from sympy import divisors
def ok(n): return '2' == max("".join(map(str, divisors(n))))
(Python)
from sympy import isprime, divisors
from itertools import count, islice, product
def agen(): # generator of terms
yield 2
for d in count(2):
for f in "12":
for mid in product("012", repeat=d-2):
for e in "12": # ending in zero has 5 as divisor
s = f+"".join(mid)+e
t = int(s)
if "2" in s and isprime(t): yield t; continue
if "2" == max("".join(map(str, divisors(t)))): yield t
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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STATUS
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approved
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