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A186309 Numbers n having more than one representation as k*(1+phi(k)/2), where phi(k) is Euler's totient function. 0
36, 540, 39852, 75418035, 113570688, 120668856, 141963360, 150836070, 18826510275, 37653020550, 106746035772831, 213492071545662, 2906980416141000, 4360470624211500, 11118121391391372 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The computations were provided by Robert Israel from sci.math.  He found no n that had three representations up to k < 10^6.  It would be a challenge to find an n with three representations.

LINKS

Table of n, a(n) for n=1..15.

Math Forum, Topic: a(1+ phi(a)/2) = b(1+phi(b)/2)

EXAMPLE

For 36, sum of the coprimes of 9 is 27, add to 9 to get 36; the sum of the coprimes of 12 is 24, add 12  to 24 to also get 36.  The corresponding {a,b} for each term is listed at the sci.math reference.

CROSSREFS

Sequence in context: A134289 A329913 A200708 * A159656 A081447 A218311

Adjacent sequences:  A186306 A186307 A186308 * A186310 A186311 A186312

KEYWORD

nonn

AUTHOR

J. M. Bergot, Feb 17 2011

EXTENSIONS

a(11)-a(15) from Donovan Johnson, Feb 21 2011

STATUS

approved

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Last modified May 26 13:59 EDT 2022. Contains 354092 sequences. (Running on oeis4.)