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A374899 a(n) is the least semiprime that starts with n.

%I A374899 #11 Jul 23 2024 20:41:40
%S A374899 10,21,33,4,51,6,74,82,9,10,111,121,133,14,15,161,177,183,194,201,21,
%T A374899 22,235,247,25,26,274,287,291,301,314,321,33,34,35,361,371,38,39,403,
%U A374899 411,422,437,445,451,46,471,481,49,501,51,526,533,542,55,562,57,58,591,6001,611,62,633,649,65,662
%N A374899 a(n) is the least semiprime that starts with n.
%H A374899 Robert Israel, <a href="/A374899/b374899.txt">Table of n, a(n) for n = 1..10000</a>
%e A374899 a(5) = 51 because 51 = 3 * 17 is a semiprime that starts with 5, and is the least such semiprime.
%p A374899 f:= proc(n) local d,x;
%p A374899   if numtheory:-bigomega(n)=2 then return n fi;
%p A374899   for d from 1 do
%p A374899     for x from n*10^d to (n+1)*10^d-1 do
%p A374899       if numtheory:-bigomega(x)=2 then return x fi
%p A374899   od od
%p A374899 end proc:
%p A374899 map(f, [$1..100]);
%Y A374899 Cf. A001358, A018800, A374897.
%K A374899 nonn,base,look
%O A374899 1,1
%A A374899 _Robert Israel_, Jul 22 2024