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 A379268 #12 Dec 20 2024 19:11:47 %S A379268 100,1001,1010,1100,10011,10101,10110,11001,11010,11100,100111,101011, %T A379268 101101,101110,110011,110101,110110,111001,111010,111100,1001111, %U A379268 1010111,1011011,1011101,1011110,1100111,1101011,1101101,1101110,1110011,1110101,1110110,1111001 %N A379268 Numbers with only digits "1" and two digits "0". %C A379268 Binary representation of A379267. %C A379268 Numbers in A007088 with two 0 digits. %F A379268 a(n) = A007088(A379267(n)). %t A379268 Select[Range[10^7],Count[IntegerDigits[#],0]==2&&Max[IntegerDigits[#]]==1&] (* _James C. McMahon_, Dec 20 2024 *) %o A379268 (Python) %o A379268 from math import isqrt, comb %o A379268 from sympy import integer_nthroot %o A379268 def A379268(n): %o A379268 a = (m:=integer_nthroot(6*n, 3)[0])+(n>comb(m+2,3))+2 %o A379268 b = isqrt((j:=comb(a,3)-n+1)<<3)+1>>1 %o A379268 c = j-comb((r:=isqrt(w:=j<<1))+(w>r*(r+1)),2)-1 %o A379268 return (10**a-1)//9-10**b-10**c %Y A379268 Cf. A007088, A379267, A023416, A357773. %K A379268 nonn,base %O A379268 1,1 %A A379268 _Chai Wah Wu_, Dec 19 2024