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Cubes c such that c + 2 and c - 2 are semiprime.
1

%I #9 Nov 23 2016 18:39:51

%S 8,216,1331,2197,4913,9261,15625,35937,59319,68921,117649,185193,

%T 421875,531441,658503,704969,1030301,1367631,3723875,5268024,5359375,

%U 11390625,13651919,16581375,17779581,19902511,23149125,25672375,29503629,36264691,38958219,40353607

%N Cubes c such that c + 2 and c - 2 are semiprime.

%C Intersection of A000578 and A105571.

%H K. D. Bajpai, <a href="/A275023/b275023.txt">Table of n, a(n) for n = 1..10000</a>

%e a(1) = 8 = 2^3. Also, 8 + 2 = 10 = 2*5; 8 - 2 = 6 = 2*3; both are semiprime.

%e a(2) = 216 = 6^3. Also, 216 + 2 = 218 = 2*109; 216 - 2 = 214 = 2*107; both are semiprime.

%t Select[Table[n^3, {n, 1000}], PrimeOmega[# + 2] == 2 && PrimeOmega[# - 2] == 2 &]

%o (PARI) for (n = 1, 1000, s = n^3; if(bigomega (s+2) == 2 && bigomega (s-2) == 2, print1 (s, ", ")))

%Y Cf. A000578, A001358, A105571, A278022.

%K nonn

%O 1,1

%A _K. D. Bajpai_, Nov 12 2016