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Semiprimes of the form 2^k - k^2.
3

%I #17 Jul 08 2023 15:23:14

%S 1927,8023,32543,2096711,8388079,137438952103,549755812367,

%T 2199023253871,8796093020359,140737488353119,562949953418911,

%U 36028797018960943,147573952589676408439,37778931862957161703943

%N Semiprimes of the form 2^k - k^2.

%H Hugo Pfoertner, <a href="/A099482/b099482.txt">Table of n, a(n) for n = 1..36</a>

%H Dario Alpern, <a href="https://www.alpertron.com.ar/ECM.HTM">Factorization using the Elliptic Curve Method.</a>

%e a(2) = 8023 because 8023 = 71*113 = 2^13 - 13^2 = 2^A099481(2) - A099481(2)^2.

%t Select[Table[2^n - n^2, {n, 100}], PrimeOmega[#] == 2&] (* _Vincenzo Librandi_, Sep 21 2012 *)

%Y Cf. A024012 2^n-n^2, A099481 2^k-k^2 is a semiprime, A072180 2^k-k^2 is prime, A075896 primes of the form 2^k-k^2.

%K nonn

%O 1,1

%A _Hugo Pfoertner_, Oct 18 2004