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 A269758 #79 Sep 08 2022 08:46:16 %S A269758 2,4,16,32,128,256,2048,8192,16384,65536,131072,524288,4194304, %T A269758 8388608,33554432,67108864,268435456,536870912,2147483648,4294967296, %U A269758 17179869184,34359738368,137438953472,274877906944,2199023255552,8796093022208,17592186044416,70368744177664 %N A269758 Prime powers with squarefree neighbors. %C A269758 All a(n) are powers of 2. %C A269758 No terms are powers of 8. - _Robert Israel_, Jan 07 2019 %H A269758 Robert Israel, <a href="/A269758/b269758.txt">Table of n, a(n) for n = 1..150</a> %e A269758 2 is in this sequence because both 2 - 1 = 1 and 2 + 1 = 3 are squarefree. %p A269758 map(t -> 2^t, select(t -> numtheory:-issqrfree(2^t-1) and numtheory:-issqrfree(2^t+1), [seq(seq(3*k+i,i=1..2),k=0..20)])); # _Robert Israel_, Jan 07 2019 %o A269758 (Magma) [2^n: n in [1..50] | IsSquarefree(2^n-1) and IsSquarefree(2^n+1)]; %Y A269758 Cf. A000961. %K A269758 nonn %O A269758 1,1 %A A269758 _Juri-Stepan Gerasimov_, Apr 30 2016