# Ambiguity in sequence A073175 First occurrence of an n-digit prime as a substring in the concatenation of the natural numbers

Jonathan Post jvospost3 at gmail.com
Fri Aug 22 22:27:21 CEST 2008

```A073175  	 First occurrence of an n-digit prime as a substring in the
concatenation of the natural numbers
12345678910111213141516171819202122232425262728293031....

Is there not a problem when the "n-digit" prime found by a greedy
algorithm is a substring starting with a zero not proper for OEIS
format, or does the definition gave to be amended to eliminate this?

By the way, the semiprime analogue would seem to be:

First occurrence of an n-digit semiprime as a substring in the
concatenation of the natural numbers
12345678910111213141516171819202122232425262728293031....

n  a(n)  comment
1    4     A001358(1)
2    34   semiprime(12)
3   123  semiprime(42)
4   1234  semiprime(363)
5   34567  semiprime(8514)
6   891011 = 11 * 81001
7   1234567 = 127 * 9721
8   10111213 = 7 * 1444459
9   910111213 = 11 * 82737383
10 3456789101 = 359 * 9628939
11 23456789101 = 37 * 633967273
12 123456789101 = 9091 * 13580111
13 6789101112131 = 13 * 522238547087
14 13141516171819 = 7 * 1877359453117
15 234567891011121 = 3 * 78189297003707
16 3456789101112131 = 1117 * 3094708237343
17 23456789101112131 = 14293 * 1641138256567
18 223242526272829303 = 2633 * 84786375340991
19 4567891011121314151 = 11 * 415262819192846741
20 34567891011121314151 = 449 * 76988621405615399

is that right?

```