login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A063512 Least number starting a chain of exactly 2n-1 consecutive integers that do not have totient-inverses. 5
3, 13, 73, 401, 241, 865, 8405, 4033, 10567, 14261, 35171, 64521, 112691, 134641, 256831, 159121, 1214533, 597081, 2277139, 1039681, 5972401, 2307317, 12033793, 9403681, 5313463, 23777761, 84502091, 19773769, 159227791, 9377213, 146793539, 114748705, 245856241 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

3*n/8*log(log(n)) < Phi(n) < n, for n > 30.

a(30) = 9377213.

LINKS

Table of n, a(n) for n=1..33.

FORMULA

a(n)=Min{x : invphi(x+j) is empty exactly for j=0..2n-2}

EXAMPLE

n=6: a(6)=865 because it is the first number initiating a chain of exactly 2.6-1=11 consecutive integers, {865,...,875}, such that each has no totient-inverse.

MATHEMATICA

a = Table[0, {5*10^7}]; Do[b = EulerPhi[n]/2; If[b < 5*10^7 + 1, a[[b]]++ ], {n, 3, 5*10^8}]; (* used to find a(7) *) Do[ If[ a[[n]] == a[[n + 1]] == a[[n + 2]] == a[[n + 3]] == a[[n + 4]] == a[[n + 5]] == a[[n + 6]] == 0, Print[2n - 1]], {n, 1, 5*10^7 -6}]

CROSSREFS

Cf. A000010, A007617, A005277.

Sequence in context: A090754 A067764 A193930 * A199317 A205776 A132846

Adjacent sequences:  A063509 A063510 A063511 * A063513 A063514 A063515

KEYWORD

nonn

AUTHOR

Labos Elemer, Aug 22 2001

EXTENSIONS

Edited and extended by Robert G. Wilson v, May 28 2002 and Jul 11 2002

David Wasserman pointed out that a(21) was incorrect and supplied a better description on Jul 10 2002

a(29) and a(31)-a(33) from Donovan Johnson, Oct 20 2011

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
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 22 07:39 EST 2020. Contains 331139 sequences. (Running on oeis4.)