A352016 Lexicographically earliest sequence of distinct positive integers such that a(n) written on top of a(n+1) forms a correct 2-integer brick (see the Comments and Example sections for an explanation).

1, 3, 7, 9, 27, 31, 11, 13, 17, 19, 37, 71, 33, 77, 39, 217, 73, 91, 79, 97, 271, 93, 277, 99, 377, 111, 113, 117, 119, 137, 171, 131, 173, 191, 177, 133, 311, 139, 317, 179, 197, 371, 193, 771, 199, 777, 313, 711, 319, 717, 331, 713, 337, 719, 397, 773, 391, 779, 917, 731, 373, 737, 379, 797, 971, 733, 911

Offset

1,2

Comments

a(15) = 39 and a(16) = 217; when we write a(15) on top of a(16) we form the "brick":

.39

217

From left to right we read (vertically) the three integers 2, 31 and 97 which are prime and thus achieve a correct 2-integer brick.

Links

Table of n, a(n) for n=1..67.

Eric Angelini, Another brick in the wall, Personal blog of the author, Feb. 2022.

Example

a(1) = 1 and a(2) = 3 form the prime 13 when red vertically from left to right;
a(2) = 3 and a(3) = 7 form the prime 37 when red vertically from left to right;
a(3) = 7 and a(4) = 9 form the prime 79 when red vertically from left to right;
a(4) = 9 and a(5) = 27 form the primes 2 and 79 when red vertically from left to right;
a(5) = 27 and a(6) = 31 form the primes 23 and 71 when red vertically from left to right; etc.

Crossrefs

Cf. A352017 (3-integer bricks).

Sequence in context: A118564 A098338 A033958 * A018827 A249664 A057840

Adjacent sequences: A352013 A352014 A352015 * A352017 A352018 A352019

Keyword

base,nonn

Author

Eric Angelini and Carole Dubois, Feb 28 2022

Status

approved