|
| |
|
|
A053249
|
|
Number of divisors of n such that n and n+1 have the same sum of divisors.
|
|
9
|
|
|
|
4, 4, 8, 8, 12, 8, 8, 4, 6, 12, 10, 4, 16, 12, 8, 8, 8, 12, 16, 8, 8, 16, 16, 16, 16, 8, 16, 8, 16, 4, 16, 16, 16, 12, 24, 12, 16, 8, 16, 16, 8, 16, 16, 12, 16, 16, 16, 16, 12, 12, 12, 16, 16, 40, 16, 16, 32, 12, 24, 32, 24, 16, 16, 24, 24, 4, 24, 16, 64, 24, 16, 8, 16, 16, 16, 24, 32, 32, 20, 16
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,1
|
|
|
LINKS
|
T. D. Noe, Table of n, a(n) for n = 1..4804
|
|
|
FORMULA
|
a(n) = tau(A002961(n))
|
|
|
MATHEMATICA
|
Reap[ Do[ If[ DivisorSigma[1, n] == DivisorSigma[1, n + 1], tau = DivisorSigma[0, n]; Print[{n, tau}]; Sow[tau]], {n, 1, 4*10^6}]][[2, 1]] (* Jean-François Alcover, Oct 08 2012 *)
DivisorSigma[0, #]&/@Flatten[Position[Partition[DivisorSigma[1, Range[ 4000000]], 2, 1], _?(First[#] == Last[#]&), {1}, Heads->False]] (* Harvey P. Dale, Jul 04 2014 *)
|
|
|
PROG
|
(PARI) do(lim)=my(v=List(), k=1, t); for(n=2, lim, t=sigma(n); if(t==k, listput(v, numdiv(n-1))); k=t); Vec(v) \\ Charles R Greathouse IV, Feb 08 2017
|
|
|
CROSSREFS
|
Cf. A000203, A000005, A002961, A053215, A054002, A054003.
Sequence in context: A105675 A196054 A292135 * A071339 A146890 A168273
Adjacent sequences: A053246 A053247 A053248 * A053250 A053251 A053252
|
|
|
KEYWORD
|
nonn,nice
|
|
|
AUTHOR
|
Asher Auel (asher.auel(AT)reed.edu) Jan 11, 2000
|
|
|
EXTENSIONS
|
More terms from Naohiro Nomoto, Mar 16 2001
|
|
|
STATUS
|
approved
|
| |
|
|
