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 A167521 #9 Jul 27 2024 13:54:44
%S A167521 11,29,47,67,85,105,123,143,161,181,182,184,187,190,193,196,199,202,
%T A167521 205,209,239,266,296,323,353,380,410,445,446,448,451,454,457,460,463,
%U A167521 467,497,527,554,584,614,641,671,701,727,728,730,733,736,739,742,745,748
%N A167521 Positive integers not occurring in A167520.
%C A167521 Equivalently, positions of zero digits in A167520 (when all terms are concatenated).
%C A167521 The first differences are (18, 18, 20, 18, 20, 18, 20, 18, 20, 1, 2, 3, 3, 3, 3, 3, 3, 3, 4, 30, 27, 30, 27, 30, 27, 30, 35, 1, 2, 3, 3, 3, 3, 3, 4, ...)
%e A167521 The first occurrence of the digit '0' in A167520 is as the least significant digit of A167520(10)=10, which occurs at position 11, thus a(1)=11. Equivalently, this is the least positive integer missing in A167520.
%e A167521 The next occurrence of the digit '0' in A167520 is at position 29 (and 29 is the second positive integer not occurring in A167520), thus a(2)=29.
%o A167521 (PARI) base(n,b=10) = { my( a=[ n%b ]); while( 0<n\=b, a=concat( n%b, a )); a }
%o A167521 {a=b=[]; for(n=1,499, #b>=n & for(i=a[n-1]+1,#b,b[i] & (a=concat(a,i)) & break); #a<n & a=concat(a,#b+1); b=concat(b,base(a[n]))); for(i=1,#b, b[i] || print1(i","))}
%Y A167521 Cf. A167500-A167503, A167520-A167523.
%K A167521 nonn,base
%O A167521 1,1
%A A167521 _M. F. Hasler_, Nov 05 2009