|
| |
|
|
A146564
|
|
a(n) is the number of solutions of the equation k*n/(k-n) = c. k,c integers.
|
|
5
|
|
|
|
1, 4, 4, 7, 4, 13, 4, 10, 7, 13, 4, 22, 4, 13, 13, 13, 4, 22, 4, 22, 13, 13, 4, 31, 7, 13, 10, 22, 4, 40, 4, 16, 13, 13, 13, 37, 4, 13, 13, 31, 4, 40, 4, 22, 22, 13, 4, 40, 7, 22, 13, 22, 4, 31, 13, 31, 13, 13, 4, 67, 4, 13, 22, 19, 13, 40, 4, 22, 13, 40, 4, 52
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
COMMENTS
|
In general if n is a prime then a(p)=4, k is from {p-1,p+1,2*p,p^2+p}, if n =p^2 then a(p^2)=7, k is from {p^2-p,p^2-1,p^2+1,p^2+p,p^3-p^2,p^3+p^2,p^4+p^2}.
The sequence counts solutions with k>0 and any sign of c, or, alternatively, solutions with c>0 and any sign of k. If solutions were constrained to k>0 and c>0, A048691 would result. [From R. J. Mathar, Nov 21 2008]
|
|
|
LINKS
|
Nathaniel Johnston, Table of n, a(n) for n = 1..10000
U. Cerruti, Percorsi tra i numeri, pages 2-4. [In Italian]
|
|
|
FORMULA
|
Conjecture: a(n) = A048691(n)+A063647(n). - R. J. Mathar, Nov 21 2008 (See Corollary 4 in Cerruti's paper.)
a(n) = Sum(d|n, psi(2^omega(d)), where psi is A001615 and omega is A001221. - Enrique Pérez Herrero, Apr 13 2012
|
|
|
EXAMPLE
|
For n=7 we search the number of integer solutions of the equation 7*k/(k-7). This holds for k from {6,8,14,56}. Then a(7)=4. For n=10 we search the number of integer solutions of the equation 10*k/(k-10). This holds for k from {5,6,8,9,11,12,14,15,20,30,35,60,110}. Then a(10)=13.
|
|
|
MAPLE
|
A146564 := proc(n) local b, d, k, c ; b := numtheory[divisors](n^2) ; kbag := {} ; for d in b do k := d+n ; if k > 0 then kbag := kbag union {k} ; fi ; k := -d+n ; if k > 0 then kbag := kbag union {k} ; fi; end do; RETURN(nops(kbag)) ; end: for n from 1 to 800 do printf("%d, ", A146564(n)) ; od: # R. J. Mathar, Nov 21 2008
|
|
|
PROG
|
(PARI)
\\ Enrique Pérez Herrero.- Apr 14 2012
jordantot(n, k)=sumdiv(n, d, d^k*moebius(n/d));
dedekindpsi(n)=jordantot(n, 2)/eulerphi(n);
A146564(n)=sumdiv(n, d, dedekindpsi(2^omega(d)));
for(n=1, 200, print(n" "A146564(n)))
|
|
|
CROSSREFS
|
Cf. A191973.
Sequence in context: A197009 A204156 A163106 * A048785 A204008 A016711
Adjacent sequences: A146561 A146562 A146563 * A146565 A146566 A146567
|
|
|
KEYWORD
|
nonn,easy
|
|
|
AUTHOR
|
Ctibor O. Zizka, Nov 01 2008
|
|
|
EXTENSIONS
|
Extended beyond a(11) by R. J. Mathar, Nov 21 2008
|
|
|
STATUS
|
approved
|
| |
|
|
