|
Search: id:A105999
|
|
|
| A105999 |
|
Semiprimeth recurrence: a(0) = 1, a(n+1) = semiprime(a(n)) = A001358(a(n)). |
|
+0
5
|
|
| 1, 4, 10, 26, 77, 235, 779, 2785, 10643, 43697, 192893, 915218, 4657929, 25380749, 147721169, 916036271, 6037442989, 42191467826, 311911160465, 2434014941905, 20007995450483
(list; graph; listen)
|
|
|
OFFSET
|
0,2
|
|
|
COMMENT
|
Semiprime equivalent of Wilson's primeth recurrence: A007097.
|
|
EXAMPLE
|
a(1) = semiprime(1) = 4.
a(2) = semiprime(semiprime(1)) = semiprime(4) = 10.
a(3) = semiprime(semiprime(semiprime(1))) = semiprime(semiprime(4)) = semiprime(10) = 26.
|
|
MATHEMATICA
|
SemiPrimePi[n_] := Sum[PrimePi[n/Prime@i] - i + 1, {i, PrimePi@ Sqrt@n}]; SemiPrime[n_] := Block[{e = Floor[Log[2, n] + 1], a, b}, a = 2^e; Do[b = 2^p; While[SemiPrimePi@a < n, a = a + b]; a = a - b/2, {p, e, 0, -1}]; a + b/2]; NestList[SemiPrime@# &, 1, 18] - from Robert G. Wilson v (rgwv(AT)rgwv.com), May 31 2006
|
|
CROSSREFS
|
Cf. A001358, A007097, A091022, A105997, A105998.
Sequence in context: A099234 A087222 A130583 this_sequence A121494 A122744 A077923
Adjacent sequences: A105996 A105997 A105998 this_sequence A106000 A106001 A106002
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 29 2005
|
|
EXTENSIONS
|
a(5)-a(15) from Robert G. Wilson v (rgwv(AT)rgwv.com), Apr 30 2005
a(16)-a(20) from Robert G. Wilson v (rgwv(AT)rgwv.com), May 31 2006
|
|
|
Search completed in 0.002 seconds
|
