A337049 - OEIS

%I #12 Feb 06 2021 21:59:34

%S 10,26,30,66,70,130,146,154,190,238,246,318,370,434,498,518,598,646,

%T 658,682,690,786,814,826,842,910,946,970,1030,1038,1066,1082,1118,

%U 1226,1246,1270,1322,1330,1346,1390,1526,1586,1606,1610,1686,1738,1758,1770,1786,1798,1914,2002,2086,2158,2198

%N Numbers k such that (k + A000010(k))/2 and (k - A000010(k))/2 are prime.

%C All terms are even and squarefree.

%H Robert Israel, <a href="/A337049/b337049.txt">Table of n, a(n) for n = 1..10000</a>

%e a(3) = 30 is in the sequence because A000010(30) = 8 and (30+8)/2 = 19 and (30-8)/2 = 11 are prime.

%p filter:= proc(n) local t; t:= numtheory:-phi(n); isprime((n+t)/2) and isprime((n-t)/2) end proc:

%p select(filter, [seq(i,i=6..10000,4)]);

%Y Cf. A000010.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Aug 12 2020