|
| |
| |
|
|
|
1, 1, 1, 2, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 2, 4, 1, 2, 1, 2, 2, 2, 1, 4, 2, 2, 2, 2, 1, 4, 1, 2, 2, 2, 2, 6, 1, 2, 2, 4, 1, 4, 1, 2, 2, 2, 1, 4, 2, 2, 2, 2, 1, 4, 2, 4, 2, 2, 1, 4, 1, 2, 2, 6, 2, 4, 1, 2, 2, 4
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,4
|
|
|
COMMENTS
| a(n) = A000010(A000005(n)) - Charles R Greathouse IV Aug 11 2009
|
|
|
FORMULA
| a(1) = 1, a(p) = 1 for p = primes (A000040), a(pq) = 2 for pq = product of two distinct primes (A006881), a(pq...z) = 2^(k-1) for pq...z = product of k (k > 2) distinct primes p, q, ..., z (A120944), a(p^(q-1) = q - 1 for p, q = primes (A000040).
|
|
|
EXAMPLE
| a(16) = a(2^(5-1)) = 5-1 = 4.
|
|
|
MATHEMATICA
| Table[EulerPhi[DivisorSigma[0, n]], {n, 1, 80}] (* Carl Najafi, Aug 15 2011 *)
|
|
|
CROSSREFS
| Sequence in context: A082477 A036430 A163377 * A128428 A056171 A076755
Adjacent sequences: A163106 A163107 A163108 * A163110 A163111 A163112
|
|
|
KEYWORD
| nonn,easy
|
|
|
AUTHOR
| Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Jul 20 2009
|
|
|
EXTENSIONS
| More terms by Carl Najafi (carlnajafi(AT)gmail.com), Aug 15 2011
|
| |
|
|
