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A066691 Value of tau(2n-1) when tau(2n-1) = tau(2n+1). 1
2, 2, 2, 2, 2, 4, 2, 4, 2, 2, 4, 4, 4, 2, 2, 4, 2, 4, 4, 2, 4, 2, 4, 4, 2, 2, 4, 4, 4, 4, 4, 4, 2, 4, 2, 6, 4, 4, 2, 2, 4, 4, 4, 2, 4, 4, 4, 4, 4, 2, 4, 4, 4, 4, 4, 2, 6, 2, 4, 4, 2, 4, 4, 6, 4, 4, 2, 4, 4, 4, 4, 2, 4, 4, 4, 2, 6, 2, 4, 6, 2, 2, 8, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 2, 4, 4, 2, 2, 6, 4, 2, 4, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harry J. Smith, Table of n, a(n) for n = 1..1000

MAPLE

with(numtheory): A066691:=n->`if`(tau(2*n-1) = tau(2*n+1), tau(2*n-1), NULL): seq(A066691(n), n=1..1000); # Wesley Ivan Hurt, Jan 03 2016

PROG

(PARI) for (n=2, 10000, if (numdiv(2*n-1) == numdiv(2*n+1), write1("tau=tau.txt", numdiv(2*n-1), ", ")))

(PARI) { n=0; for (m=1, 10^10, if ((d=numdiv(2*m-1)) == numdiv(2*m+1), write("b066691.txt", n++, " ", d); if (n==1000, return)) ) } \\ Harry J. Smith, Mar 17 2010

(MAGMA) [NumberOfDivisors(2*n-1): n in [1..400] | NumberOfDivisors(2*n-1) eq NumberOfDivisors(2*n+1)]; // Vincenzo Librandi, Jan 04 2016

CROSSREFS

Cf. A000005 (tau).

Sequence in context: A104361 A211449 A086876 * A260123 A319411 A164296

Adjacent sequences:  A066688 A066689 A066690 * A066692 A066693 A066694

KEYWORD

nonn

AUTHOR

Jon Perry, Jan 11 2002

EXTENSIONS

Offset changed from 0 to 1 by Harry J. Smith, Mar 17 2010

STATUS

approved

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Last modified October 28 02:02 EDT 2021. Contains 348305 sequences. (Running on oeis4.)