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A053249 Number of divisors of n such that n and n+1 have the same sum of divisors. 10
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
Amiram Eldar, Table of n, a(n) for n = 1..10135 (from the b-file at A002961; terms 1..4804 from T. D. Noe)
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 *)
DivisorSigma[0, #]&/@(SequencePosition[DivisorSigma[1, Range[4000000]], {x_, x_}][[All, 1]]) (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Jul 25 2019 *)
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
(Magma) [#Divisors(n):n in [1..4000000]| SumOfDivisors(n) eq SumOfDivisors(n+1)]; // Marius A. Burtea, Sep 07 2019
CROSSREFS
Sequence in context: A105675 A196054 A292135 * A071339 A146890 A168273
KEYWORD
nonn,nice
AUTHOR
Asher Auel, Jan 11 2000
EXTENSIONS
More terms from Naohiro Nomoto, Mar 16 2001
STATUS
approved

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Last modified June 23 09:34 EDT 2024. Contains 373629 sequences. (Running on oeis4.)