A363374 Numbers k such that 2^k - 3 is a semiprime.

8, 11, 13, 15, 17, 18, 21, 23, 25, 30, 32, 33, 34, 35, 36, 37, 40, 44, 54, 58, 60, 61, 71, 73, 92, 95, 101, 102, 106, 144, 160, 164, 183, 200, 209, 210, 216, 241, 244, 270, 273, 274, 281, 293, 309, 313, 344, 365, 422, 430, 461, 475, 477, 480, 504, 509, 556, 579, 597, 609, 612, 631, 650

Offset

1,1

Comments

The numbers 717, 720, 759 are also terms with 713 being the only remaining unknown below them.

Links

Table of n, a(n) for n=1..63.

Example

11 is a member because 2^11 - 3 = 2045 = 5 * 409 is a semiprime.

Mathematica

Select[Range[700], PrimeOmega[2^#-3]==2&] (* Harvey P. Dale, Dec 14 2024 *)

Crossrefs

Cf. A085724.

Sequence in context: A191887 A122195 A064153 * A337491 A106670 A247463

Adjacent sequences: A363371 A363372 A363373 * A363375 A363376 A363377

Keyword

nonn,changed

Author

Kevin P. Thompson, May 29 2023

Status

approved