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 A344783 #7 Sep 23 2024 12:31:58
%S A344783 1,3,4,7,18,25,26,30,40,50,95,150,348,694,1052,1222,1808,2567,4917,
%T A344783 5399,7438,10720,12152,30412,38313,53620,121419,123523
%N A344783 Numbers k such that 1 + Sum_{i=1..k} floor(k/i)*(2^i) is a prime number.
%C A344783 Equivalently, numbers k such that A168512(2^k) is a prime number.
%C A344783 The corresponding primes are 3, 19, 41, 283, 525529, 67117859, 134234921, 2147551801, ...
%C A344783 If k is a term of this sequence then 2^k * A168512(2^k) is a term of A168654 (see _Ray Chandler_'s comment in A168654).
%e A344783 1 is a term since 1 + Sum_{i=1..1} floor(k/i)*(2^i) = 1 + 2 = 3 is a prime.
%e A344783 3 is a term since 1 + Sum_{i=1..3} floor(k/i)*(2^i) = 1 + 6 + 4 + 8 = 19 is a prime.
%t A344783 Select[Range[100], PrimeQ[1 + Sum[Floor[#/i]*2^i,{i, 1, #}]] &]
%Y A344783 Cf. A168512, A168654.
%K A344783 nonn,more
%O A344783 1,2
%A A344783 _Amiram Eldar_, May 28 2021
%E A344783 a(27)-a(28) from _Michael S. Branicky_, Sep 23 2024