A303847 Lexicographically earliest sequence of distinct terms such that what emerges from the mask (right-aligned) is prime (see the Comments section for the mask explanation).

1, 20, 2, 21, 3, 22, 4, 23, 5, 24, 6, 25, 7, 26, 8, 27, 9, 28, 200, 10, 201, 11, 202, 12, 203, 13, 204, 14, 205, 15, 206, 16, 207, 17, 208, 18, 209, 19, 210, 29, 211, 30, 212, 31, 213, 32, 214, 33, 215, 34, 216, 35, 217, 36, 218, 37, 219, 38, 220, 39, 221, 40, 222, 41, 223, 42, 224, 43, 225, 44, 226, 45, 227, 46, 228, 47

Offset

1,2

Comments

For any pair of consecutive terms, one of the terms uses fewer digits than the other. This term is called the mask. Put the mask on the other term, starting from the right. What is not covered by the mask forms a prime number on the left.

The sequence starts with a(1) = 1 and is always extended with the smallest integer not yet present that doesn't lead to a contradiction.

This sequence is a permutation of the positive integers, as all integers will appear at some point, either as mask or masked.

Links

Jean-Marc Falcoz, Table of n, a(n) for n = 1..10001

Example

In the pair (1,20), 1 is the mask; 2 emerges and is prime;
in the pair (20,2), 2 is the mask; 2 emerges and is prime;
in the pair (2,21), 2 is the mask; 2 emerges and is prime;
in the pair (21,3), 3 is the mask; 2 emerges and is prime;
...
in the pair (117,2018), 117 is the mask; 2 emerges and is prime;
etc.

Crossrefs

Cf. A303782 (same idea, but the mask is left-aligned).

Sequence in context: A037926 A040397 A040398 * A303849 A277981 A040399

Adjacent sequences: A303844 A303845 A303846 * A303848 A303849 A303850

Keyword

nonn,base

Author

Eric Angelini and Jean-Marc Falcoz, May 01 2018

Status

approved