A289117 Numbers k such that 155*2^k + 1 is a semiprime.

3, 4, 6, 9, 13, 16, 18, 21, 43, 47, 63, 70, 77, 83, 87, 97, 109, 117, 119, 126, 127, 133, 143, 149, 169, 171, 251, 277, 281, 283, 287, 313, 329, 351, 393, 429, 450, 460, 577, 587, 593, 610, 616, 679, 689

Offset

1,1

Comments

a(35) > 392. - Robert Price, Jul 21 2017

Links

Table of n, a(n) for n=1..45.

Example

3 is a term because 155*2^3 + 1 = 1241 = 17*73.

Mathematica

Select[Range[200], PrimeOmega[155 2^# + 1] == 2 &]

Prog

(Magma) [n: n in [2..200] | &+[d[2]: d in Factorization(155*2^n+1)] eq 2];

Crossrefs

Cf. A032454.

Sequence in context: A285303 A135072 A032720 * A355697 A167928 A090867

Adjacent sequences: A289114 A289115 A289116 * A289118 A289119 A289120

Keyword

nonn,more

Author

Vincenzo Librandi, Jun 25 2017

Extensions

a(27)-a(34) from Robert Price, Jul 21 2017

a(35)-a(45) from Tyler Busby, Feb 17 2023

Status

approved