A352017 Lexicographically earliest sequence of distinct positive integers such that a(n) written on top of a(n+1) which in turn is written on top of a(n+2) form a correct 3-integer brick (see the Comments and Example sections for an explanation).

1, 2, 7, 21, 9, 3, 27, 33, 39, 17, 11, 239, 13, 37, 19, 77, 31, 99, 71, 79, 231, 91, 73, 211, 93, 97, 213, 313, 331, 111, 113, 337, 119, 117, 2331, 179, 131, 339, 171, 139, 333, 177, 133, 393, 771, 311, 993, 711, 191, 913, 197, 173, 319, 797, 317, 2313, 733, 371, 391, 773, 377, 933, 739, 717, 2311, 939, 713

Offset

1,2

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, a(2) = 2 and a(3) = 7 stacked form the prime number 127, which is what we want;
a(2) = 2, a(3) = 7 and a(4) = 21 stacked form the hereunder "brick":
.2
.7
21
From left to right we read (vertically) the two integers 2 and 271 which are prime and thus achieve a correct 3-integer brick;
a(3) = 7, a(4) = 21 and a(5) = 9 stacked form the hereunder "brick":
.7
21
.9
From left to right we read (vertically) the two integers 2 and 719 which are prime and thus achieve a correct 3-integer brick;
(...)
a(n) = 1739, a(n+1) = 997 and a(n+2) = 1771 stacked form the hereunder "brick":
1739
.997
1771
From left to right we read (vertically) the four integers 11, 797, 397 and 971 which are prime and thus achieve a correct 3-integer brick; etc.

Crossrefs

Cf. A352016 (2-integer bricks).

Sequence in context: A139012 A132605 A088157 * A265316 A079034 A265500

Adjacent sequences: A352014 A352015 A352016 * A352018 A352019 A352020

Keyword

base,nonn

Author

Carole Dubois and Eric Angelini, Feb 28 2022

Status

approved