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

1,1

Comments

The numbers 806 and 811 are also terms with 770 being the only remaining unknown below them.

Links

Table of n, a(n) for n=1..57.

Example

13 is a term because 2^13 - 5 = 8187 = 3 * 2729 is a semiprime.

Prog

(PARI) isA363491(k) = bigomega(2^k-5) == 2; \\ Hugo Pfoertner, Jun 25 2023

Crossrefs

Cf. A001358, A085724, A363374.

Sequence in context: A194408 A376298 A057930 * A342581 A353443 A332480

Adjacent sequences: A363488 A363489 A363490 * A363492 A363493 A363494

Keyword

nonn

Author

Kevin P. Thompson, Jun 05 2023

Status

approved