A270074 Select a pair of successive terms a and b; switch the two digits in contact with the comma between a and b; the new pair is now made of prime numbers. By decree no term is repeated in the sequence and all terms are nonprime numbers. This sequence is the lexicographically first with those properties.

1, 21, 33, 77, 9, 27, 39, 111, 301, 703, 91, 707, 93, 711, 99, 729, 737, 309, 741, 303, 713, 913, 117, 319, 119, 341, 731, 339, 129, 747, 333, 147, 901, 749, 371, 351, 357, 343, 717, 909, 753, 153, 159, 141, 903, 759, 171, 363, 767, 133, 183, 189, 177, 361, 763, 917, 143, 931, 779

Offset

1,2

Comments

Numbers that are composite for all last digits 1..9 cannot be part of the sequence, e.g., 201..209, 321..329. (Cf. A078492)

Links

Lars Blomberg, Table of n, a(n) for n = 1..10000

Example

The first pair of nonprime numbers is 1,21. After we switch the digits of 1,21 we get 2,11 (which are indeed both prime numbers). The second pair 21,33 (both nonprime numbers) becomes 23,13 (prime numbers). The third pair 33,77 (both nonprime numbers) becomes 37,37 (prime numbers), etc.

Crossrefs

Sequence in context: A280878 A033901 A033656 * A350099 A032792 A146902

Adjacent sequences: A270071 A270072 A270073 * A270075 A270076 A270077

Keyword

nonn,base

Author

Eric Angelini and Lars Blomberg, Mar 10 2016

Status

approved