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 A174166 #8 May 21 2023 19:23:39 %S A174166 4,6,9,10,12,15,16,21,22,24,27,30,34,36,40,42,45,49,51,52,54,55,57,64, %T A174166 66,69,70,75,76,82,84,87,90,91,96,99,100,106,112,114,115,117,120,121, %U A174166 126,129,132,135,136,141,142,147,154,156,159,166,169,174,175,177,180 %N A174166 Composites n such that 2*n-1 is prime. %H A174166 Harvey P. Dale, <a href="/A174166/b174166.txt">Table of n, a(n) for n = 1..1000</a> %e A174166 a(1)=4 because 2*4-1=7=prime; a(2)=6 because 2*6-1=11=prime. %t A174166 Select[(#+1)/2&/@Prime[Range[2,100]],CompositeQ] (* _Harvey P. Dale_, May 21 2023 *) %Y A174166 Cf. A002808. %K A174166 nonn %O A174166 1,1 %A A174166 _Juri-Stepan Gerasimov_, Mar 10 2010 %E A174166 Entries checked by _R. J. Mathar_, Apr 26 2010