A186309 Numbers n having more than one representation as k*(1+phi(k)/2), where phi(k) is Euler's totient function.

36, 540, 39852, 75418035, 113570688, 120668856, 141963360, 150836070, 18826510275, 37653020550, 106746035772831, 213492071545662, 2906980416141000, 4360470624211500, 11118121391391372

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