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 A206286 #14 Dec 10 2024 09:57:36 %S A206286 1,10,12,14,15,16,18,100,102,104,105,106,108,110,111,112,114,115,116, %T A206286 117,118,119,120,121,122,123,124,125,126,128,129,130,132,133,134,135, %U A206286 136,138,140,141,142,143,144,145,146,147,148,150,152,153,154,155,156,158 %N A206286 Nonprime numbers starting with a digit 1. %C A206286 Complement of A045707 with respect to A131835. Supersequence of A206288. %t A206286 Select[Range[200], ! PrimeQ[#] && IntegerDigits[#][[1]] == 1 &] (* _T. D. Noe_, Feb 13 2012 *) %o A206286 (Python) %o A206286 from sympy import primepi %o A206286 def A206286(n): %o A206286 def f(x): return n-1+x+((m:=10**(l:=len(str(x))-1))-(k:=min((m<<1)-1,x))-primepi(m-1)+primepi(k))-sum((m:=10**i)+primepi(m-1)-primepi((m<<1)-1) for i in range(l)) %o A206286 m, k = n, f(n) %o A206286 while m != k: m, k = k, f(k) %o A206286 return m # _Chai Wah Wu_, Dec 10 2024 %Y A206286 Cf. A045707 (primes with first digit 1), A131835 (numbers starting with a digit 1). %Y A206286 Cf. A206288. %K A206286 nonn,base %O A206286 1,2 %A A206286 _Jaroslav Krizek_, Feb 12 2012