A358130 - OEIS

%I #12 Nov 10 2022 07:43:25

%S 1,2,3,6,9,11,15,45,51,59,81,126,165,174,179,255,681,831,839,921,1734,

%T 1739,1845,2499,2519,2661,3119,5061,5094,5099,5289,5301,8061,8571,

%U 8579,9654,9659,11094,11399,12315,13254,16011,16379,18225,18234,18239,19401,19689,26214,26219,27141,28554,29039

%N Indices k such that A358128(k) is a square.

%H Robert Israel, <a href="/A358130/b358130.txt">Table of n, a(n) for n = 1..870</a>

%e a(5) = 9 is a term because A358128(9) = 25 = 5^2 is a square.

%p f:= proc(n) local p;

%p   p:= 1:

%p   do

%p     p:= nextprime(p);

%p     if isprime(p+4*n) and numtheory:-bigomega(p+2*n) = 2 then return p+2*n fi

%p   od

%p end proc:

%p select(t -> issqr(f(t)), [$1..30000]);

%o (PARI) isok(k) = my(x=2*k+2); while ((bigomega(x)!=2) || !isprime(x-2*k) || !isprime(x+2*k), x++); issquare(x); \\ _Michel Marcus_, Oct 31 2022

%Y Cf. A358128.

%K nonn

%O 1,2

%A _J. M. Bergot_ and _Robert Israel_, Oct 30 2022