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 A174099 #13 Sep 02 2024 08:39:58
%S A174099 1,2,3,4,6,7,8,12,21,25,29,38,44,55,84,93,106,136,191,211,232,378,422,
%T A174099 483,539,1272,1470,2014,2111,4144,5359,6543,13006,13632,18802,28547,
%U A174099 39420,51327,59982,62947,66875,78156,91466,113675,132938,148273,193541
%N A174099 Indices of primes of the form 2^t*3^u + 1 in the primes.
%C A174099 Numbers k such that 2^t*3^u + 1 = prime(k).
%H A174099 Amiram Eldar, <a href="/A174099/b174099.txt">Table of n, a(n) for n = 1..166</a>
%F A174099 a(n) = A000720(A005109(n)).
%e A174099 a(1) = 1 because 2^0 * 3^0 + 1 = 2 = prime(1).
%e A174099 a(2) = 2 because 2^1 * 3^0 + 1 = 3 = prime(2).
%t A174099 With[{lim = 10^7}, PrimePi[Select[Sort@ Flatten@ Table[2^i * 3^j + 1, {i, 0, Log2[lim]}, {j, 0, Log[3, lim/2^i]}], PrimeQ]]] (* _Amiram Eldar_, Sep 02 2024 *)
%o A174099 (PARI) lista(lim) = {my(s = List()); for(i = 0, logint(lim, 2), for(j = 0, logint(lim >> i, 3), listput(s, 2^i * 3^j + 1))); s = Set(s); for(i = 1, #s, if(isprime(s[i]), print1(primepi(s[i]), ", ")));} \\ _Amiram Eldar_, Sep 02 2024
%Y A174099 Cf. A000720, A005109.
%K A174099 nonn
%O A174099 1,2
%A A174099 _Juri-Stepan Gerasimov_, Mar 07 2010
%E A174099 Corrected and extended by _Charles R Greathouse IV_, Mar 21 2010