A363491 Numbers k such that 2^k - 5 is a semiprime.
7, 13, 14, 16, 19, 28, 30, 31, 40, 42, 51, 54, 55, 58, 62, 68, 85, 88, 96, 111, 112, 116, 128, 148, 160, 162, 188, 192, 198, 220, 222, 236, 242, 276, 300, 318, 319, 320, 332, 372, 373, 398, 420, 428, 432, 458, 460, 482, 505, 520, 532, 542, 546, 556, 650, 692, 714
Offset: 1
Keywords
Examples
13 is a term because 2^13 - 5 = 8187 = 3 * 2729 is a semiprime.
Programs
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Mathematica
Select[Range[715],PrimeOmega[2^#-5]==2&] (* Harvey P. Dale, Apr 22 2025 *)
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PARI
isA363491(k) = bigomega(2^k-5) == 2; \\ Hugo Pfoertner, Jun 25 2023
Comments