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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A384979 a(n) is the smallest (n+2)-digit prime consisting of a string of n identical digits d sandwiched between two digits different from d, or -1 if no such prime exists.

Table of values

n a(n)
0 11
1 101
2 1009
3 10007
4 100003
5 1000003
6 13333339
7 100000007
8 1000000007
9 13333333339
10 100000000003
11 1333333333337
12 13333333333339
13 122222222222227
14 1555555555555553
15 16666666666666661
16 100000000000000003
17 1000000000000000003
18 15555555555555555557

List of values

[11, 101, 1009, 10007, 100003, 1000003, 13333339, 100000007, 1000000007, 13333333339, 100000000003, 1333333333337, 13333333333339, 122222222222227, 1555555555555553, 16666666666666661, 100000000000000003, 1000000000000000003, 15555555555555555557]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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