|
| |
|
|
A268110
|
|
Numbers k such that (2^k-k+1)*2^k+1 is a semiprime.
|
|
1
|
|
|
|
3, 4, 6, 9, 10, 15, 19, 22, 26, 34, 47, 55, 67, 69, 72, 92, 100, 117, 160
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
LINKS
|
Table of n, a(n) for n=1..19.
|
|
|
EXAMPLE
|
a(1) = 3 because 6*8 +1 = 49 = 7*7, which is semiprime.
a(2) = 4 because 13*16+1 = 209 = 11*19, which is semiprime.
|
|
|
MAPLE
|
A268110:=n->`if`(numtheory[bigomega]((2^n-n+1)*2^n+1)=2, n, NULL): seq(A268110(n), n=1..80); # Wesley Ivan Hurt, Jan 30 2016
|
|
|
MATHEMATICA
|
Select[Range[105], PrimeOmega[(2^# - # + 1) 2^# + 1] == 2 &]
|
|
|
PROG
|
(Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [2..105]| IsSemiprime(s) where s is (2^n-n+1)*2^n+1];
(PARI) lista(nn) = {for(n=1, nn, if(bigomega((2^n-n+1)*2^n+1) == 2, print1(n, ", "))); } \\ Altug Alkan, Feb 07 2016
|
|
|
CROSSREFS
|
Cf. A201360: n for which (2^n-n+1)*2^n+1 is prime.
Sequence in context: A245810 A054686 A005214 * A124093 A025061 A284741
Adjacent sequences: A268107 A268108 A268109 * A268111 A268112 A268113
|
|
|
KEYWORD
|
nonn,more
|
|
|
AUTHOR
|
Vincenzo Librandi, Jan 30 2016
|
|
|
EXTENSIONS
|
a(18)-a(19) from Daniel Suteu, Aug 05 2019
|
|
|
STATUS
|
approved
|
| |
|
|
