A352016 - OEIS

%I #12 Jun 01 2022 12:12:21

%S 1,3,7,9,27,31,11,13,17,19,37,71,33,77,39,217,73,91,79,97,271,93,277,

%T 99,377,111,113,117,119,137,171,131,173,191,177,133,311,139,317,179,

%U 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

%N 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).

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

%C .39

%C 217

%C 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.

%H Eric Angelini, <a href="http://cinquantesignes.blogspot.com/2022/02/another-brick-in-wall.html">Another brick in the wall</a>, Personal blog of the author, Feb. 2022.

%e a(1) = 1 and a(2) = 3 form the prime 13 when red vertically from left to right;

%e a(2) = 3 and a(3) = 7 form the prime 37 when red vertically from left to right;

%e a(3) = 7 and a(4) = 9 form the prime 79 when red vertically from left to right;

%e a(4) = 9 and a(5) = 27 form the primes 2 and 79 when red vertically from left to right;

%e a(5) = 27 and a(6) = 31 form the primes 23 and 71 when red vertically from left to right; etc.

%Y Cf. A352017 (3-integer bricks).

%K base,nonn

%O 1,2

%A _Eric Angelini_ and _Carole Dubois_, Feb 28 2022