A066171 Numbers n such that d(n) = phi(n+1) - phi(n), where d(n) denotes the number of divisors of n.

6, 74, 315, 344, 5313, 17534, 23655, 27027, 46035, 54494, 56865, 139814, 13437105, 454166115, 2403502647, 4590102525, 38645268615, 96891671331

Offset

1,1

Comments

These are the n at which phi(n) is increasing at a rate equal to d(n).

a(19) > 2*10^11. - Donovan Johnson, Jun 23 2010

Links

Table of n, a(n) for n=1..18.

Example

d(74) = 4 = 40 - 36 = phi(75) - phi(74).

Mathematica

Select[ Range[ 1, 10^6 ], EulerPhi[ # + 1 ] - EulerPhi[ # ] == DivisorSigma[ 0, # ] & ]

Crossrefs

Sequence in context: A168603 A244689 A058793 * A269647 A232330 A269337

Adjacent sequences: A066168 A066169 A066170 * A066172 A066173 A066174

Keyword

nonn

Author

Joseph L. Pe, Dec 14 2001

Extensions

a(13) from Harry J. Smith, Feb 04 2010

a(14)-a(18) from Donovan Johnson, Jun 23 2010

Status

approved