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 A237989 #29 Jun 24 2024 08:47:46 %S A237989 2,6,18,26,34,42,50,70,74,78,86,98,106,110,130,138,150,158,162,170, %T A237989 198,214,218,222,234,238,242,246,250,258,262,270,278,286,290,310,314, %U A237989 334,354,358,370,382,390,394,402,406,442,450,454,462,470,474,478,490,502 %N A237989 Numbers m such that the numbers of primes, even positive integers and odd positive integers less than or equal to m are all odd. %H A237989 Ivan N. Ianakiev, <a href="/A237989/b237989.txt">Table of n, a(n) for n = 1..10000</a> %F A237989 Intersection of A042963 (odd number of odd numbers), A042964 (odd number of even numbers), A057812 (odd number of primes). - _Michel Marcus_, Feb 26 2014 %e A237989 A cubic die whose faces are marked with the numbers from 1 to 6 has odd number of sides marked with prime numbers (2, 3 and 5), even integers (2, 4 and 6) and odd integers (1, 3 and 5). Therefore, 6 is in the sequence. %t A237989 Select[Range[2, 1000, 4], OddQ[PrimePi[#]] &] (* _Paolo Xausa_, Jun 24 2024 *) %o A237989 (PARI) isok(n) = (primepi(n) % 2) && ((n % 4) == 2); \\ _Michel Marcus_, Mar 12 2014 %Y A237989 Cf. A042963, A042964, A057812, A237990. %K A237989 nonn,easy %O A237989 1,1 %A A237989 _Ivan N. Ianakiev_, Feb 16 2014