login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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-Fran├žois 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 22 03:52 EDT 2018. Contains 316431 sequences. (Running on oeis4.)