This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A343765 #7 May 01 2021 02:14:07 %S A343765 1,9,8,10,14,15,143,142,140,141,133,132,134,135,391,390,388,384,385, %T A343765 387,386,394,395,393,392,396,398,399,415,414,412,413,405,404,406,407, %U A343765 403,402,400,408,410,411,475,474,472,473,477,476,478,470,471,469,468,464 %N A343765 Lexicographically earliest sequence of distinct nonprime numbers such that for any n > 0, a(n+1) = a(n) XOR 2^k for some k >= 0 as small as possible (where XOR denotes the bitwise XOR operator). %C A343765 This sequence is similar to A003188 and to A059459; here we deal with nonprime numbers, there with integers and prime numbers, respectively. %C A343765 Will the value 4 ever appear? %H A343765 Rémy Sigrist, <a href="/A343765/b343765.txt">Table of n, a(n) for n = 1..10000</a> %H A343765 <a href="/index/Bi#binary">Index entries for sequences related to binary expansion of n</a> %e A343765 The first terms, alongside their binary expansion, are: %e A343765 n a(n) bin(a(n)) %e A343765 -- ---- --------- %e A343765 1 1 1 %e A343765 2 9 1001 %e A343765 3 8 1000 %e A343765 4 10 1010 %e A343765 5 14 1110 %e A343765 6 15 1111 %e A343765 7 143 10001111 %e A343765 8 142 10001110 %e A343765 9 140 10001100 %e A343765 10 141 10001101 %e A343765 11 133 10000101 %e A343765 12 132 10000100 %e A343765 13 134 10000110 %e A343765 14 135 10000111 %e A343765 15 391 110000111 %e A343765 16 390 110000110 %e A343765 17 388 110000100 %e A343765 18 384 110000000 %e A343765 19 385 110000001 %e A343765 20 387 110000011 %o A343765 (PARI) s=2^0; v=1; for (n=1, 54, print1 (v", "); s+=2^v; for (x=0, oo, if (!bittest(s, w=bitxor(v, 2^x)) && !isprime(w), v=w; break))) %Y A343765 Cf. A003188, A018252, A059459. %K A343765 nonn,base %O A343765 1,2 %A A343765 _Rémy Sigrist_, Apr 28 2021