|
Search: id:A091424
|
|
|
| A091424 |
|
Numbers n such that n#*2^n + 1 is prime, where n# is product of prime numbers (primorial). |
|
+0
1
|
|
| 1, 3, 4, 6, 10, 30, 31, 98, 156, 230, 432, 490
(list; graph; listen)
|
|
|
OFFSET
|
1,2
|
|
|
COMMENT
|
1# = 2 2# = 2*3 = 6 3# = 2*3*5 = 30
|
|
EXAMPLE
|
a(1)=1 because 1#*2^1 + 1 = 5 is prime
a(2)=3 because 3#*2^3 + 1 = 241 is prime
|
|
PROGRAM
|
(PARI) pp(n)=s=1; for(i=1, n, s=s*prime(i)); return(s); f(n)=pp(n)*2^n +1; for (i=1, 500, if(isprime(f(i)), print(i)))
|
|
CROSSREFS
|
Sequence in context: A103049 A103016 A061032 this_sequence A092839 A047413 A115018
Adjacent sequences: A091421 A091422 A091423 this_sequence A091425 A091426 A091427
|
|
KEYWORD
|
hard,more,nonn
|
|
AUTHOR
|
Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 02 2004
|
|
|
Search completed in 0.002 seconds
|
