OFFSET
0,1
COMMENTS
By placing one digit on both sides of n (1..9 on the left and on the right) one gets 81 different numbers that might be semiprimes. If none of these numbers is a semiprime then a(n) = 0.
The smallest n such that a(n) = 0 is 20056492. - Donovan Johnson, Feb 01 2011
If one or more digits are allowed on both sides of n, the smallest semiprime containing 20056492 is 10200564926 = 2*5100282463.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
EXAMPLE
a(23) = 1234 = 2 * 617 has the embedded substring 1"23"4.
MAPLE
a:= proc(n) local i, j, k;
for i to 9 do
for j to 9 do
k:= parse(cat(i, n, j));
if not isprime(k) and add(t[2], t=ifactors(k)[2])=2
then return k fi
od
od; return 0;
end:
seq(a(n), n=0..60); # Alois P. Heinz, Feb 01 2011
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Jonathan Vos Post, Jan 31 2011
EXTENSIONS
More terms from Alois P. Heinz, Feb 01 2011
STATUS
approved