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A109686
Smallest number beginning with the digits of n that has exactly n prime factors (counted with multiplicity).
1
11, 21, 30, 40, 500, 64, 704, 864, 9072, 1024, 11264, 120832, 133120, 143360, 1505280, 163840, 1720320, 18063360, 1966080, 20054016, 210567168, 22020096, 231211008, 243269632, 254803968, 2600468480, 2751463424, 28028436480, 2952790016, 30576476160, 31138512896, 32614907904, 330225942528
OFFSET
1,1
LINKS
EXAMPLE
a(5)=500 since 500 has prime factorization 500=2*2*5*5*5 (5 factors) and begins with 5 and is the smallest such number.
MAPLE
f:= proc(n) uses priqueue;
local pq, d, t, v, dv, i, p;
d:= ilog10(n);
initialize(pq);
insert([-2^n, 2, n], pq);
do
t:= extract(pq);
v:= -t[1];
dv:= ilog10(v);
if floor(v/10^(dv-d))=n then return v fi;
p:= nextprime(t[2]);
for i from 1 to t[3] do
insert([t[1]*(p/t[2])^i, p, i], pq);
od;
od;
end proc:
map(f, [$1..40]); # Robert Israel, Jul 23 2024
CROSSREFS
Sequence in context: A195100 A125164 A101223 * A077522 A308232 A049201
KEYWORD
base,nonn
AUTHOR
Erich Friedman, Aug 07 2005
EXTENSIONS
a(24)-a(33) from Donovan Johnson, Apr 27 2008
STATUS
approved