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 A099861 #29 Nov 15 2024 09:04:36 %S A099861 4,8,10,14,16,20,22,25,27,30,33,35,38,40,44,46,49,51,54,56,58,62,64, %T A099861 66,69,72,75,77,80,82,85,87,90,92,94,96,99,102,105,108,111,114,116, %U A099861 118,120,122,124,126,129,132,134,136,140,142,144,146,148,152,154,156,159,161 %N A099861 a(n) = (2*n-1)-st composite number: a bisection of A002808. %H A099861 A.H.M. Smeets, <a href="/A099861/b099861.txt">Table of n, a(n) for n = 1..20000</a> %F A099861 a(n) = A175228(n+1). - _A.H.M. Smeets_, Aug 19 2019 %e A099861 a(1) = 4 is the first composite number. %p A099861 b:=proc(n) if isprime(n)=true then else n fi end: B:=[seq(b(n),n=2..250)]: seq(B[2*m-1],m=1..75); # _Emeric Deutsch_, Dec 09 2004 %t A099861 Partition[Select[Range[200], CompositeQ], 2][[All, 1]] (* _Jean-François Alcover_, Mar 22 2023 *) %o A099861 (Python) %o A099861 from sympy import composite %o A099861 def A099861(n): return composite((n<<1)-1) # _Chai Wah Wu_, Nov 14 2024 %Y A099861 Cf. A002808, A099862, A175228. %K A099861 nonn,easy %O A099861 1,1 %A A099861 _N. J. A. Sloane_, Nov 19 2004 %E A099861 More terms from _Emeric Deutsch_, Dec 09 2004