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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
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
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
KEYWORD
base,nonn
AUTHOR
Eric Angelini and Carole Dubois, Feb 28 2022
STATUS
approved