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 A374845 #10 Jan 05 2025 19:51:42
%S A374845 3,6,7,11,14,19,22,23,31,38,43,46,47,59,62,67,71,79,83,86,94,103,107,
%T A374845 118,127,131,134,139,142,151,158,163,166,167,179,191,199,206,211,214,
%U A374845 223,227,239,251,254,262,263,271,278,283,302,307,311,326,331,334,347,358,359,367,379,382,383,398
%N A374845 The numbers p or 2p with p prime and p = 3 mod 4, in ascending order.
%C A374845 Numbers appearing exactly once in a Pythagorean triple and as the smallest number in this triple.
%C A374845 Subsequence of A292762.
%C A374845 Inserting 4 as second term gives A374846.
%H A374845 A. Tripathi, <a href="https://web.archive.org/web/2024*/https://www.fq.math.ca/Papers1/46_47-4/Tripathi.pdf">On Pythagorean triples containing a fixed integer</a>, Fib. Q., 46/47 (2008/2009), 331-340. See Theorem 8.
%t A374845 t={}; Do[If[(PrimeQ[n]&&Mod[n, 4] == 3)||(PrimeQ[n/2]&&Mod[n/2, 4] == 3), t=Join[t,{n}]], {n, 470}]; t
%t A374845 (* Positions of the ones in A046081, omitting position = 4; based on program by Jean-François Alcover *)
%t A374845 a[1] = 0; a[n_] := Module[{f}, f = Select[FactorInteger[n], Mod[#[[1]], 4] == 1 &][[All, 2]]; (DivisorSigma[0, If[OddQ[n], n, n/2]^2] - 1)/2 + (Times @@ (2*f + 1) - 1)/2]; arr = Array[a, nmax]; fl = Flatten[Position[arr, 1]]; Delete[fl, 2]
%Y A374845 Cf. A374846, A292762, A046081.
%K A374845 nonn
%O A374845 1,1
%A A374845 _Manfred Boergens_, Jul 22 2024