|
|
A217384
|
|
Numbers n such that 9^n + 4 is prime.
|
|
4
|
|
|
0, 1, 3, 5, 11, 15, 21, 87, 99, 281, 497, 2919, 6849, 7365, 8483, 49317, 58611
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
COMMENTS
|
Contribution from Bruno Berselli, Oct 04 2012: (Start)
Contains exactly the halved even terms of A058958.
Naturally, apart from the first term, these numbers are odd since (10-1)^(2n)+4 is divisible by 5. (End)
a(18) > 10^5. - Tyler NeSmith, May 05 2021
|
|
LINKS
|
Table of n, a(n) for n=1..17.
|
|
MATHEMATICA
|
Select[Range[0, 3000], PrimeQ[9^# + 4] &]
|
|
PROG
|
(PARI) is(n)=ispseudoprime(9^n+4) \\ Charles R Greathouse IV, Feb 20 2017
|
|
CROSSREFS
|
Cf. A058958, A090649.
Sequence in context: A105772 A244520 A034169 * A335279 A136977 A003529
Adjacent sequences: A217381 A217382 A217383 * A217385 A217386 A217387
|
|
KEYWORD
|
nonn,hard,more
|
|
AUTHOR
|
Vincenzo Librandi, Oct 04 2012
|
|
EXTENSIONS
|
a(13)-a(14) from Bruno Berselli, Oct 04 2012
a(15)-a(17) from Tyler NeSmith, May 05 2021
|
|
STATUS
|
approved
|
|
|
|