In mathematics, specifically number theory, a sparsely totient number is a natural number, n, such that for all m > n,
:<math>\varphi(m)>\varphi(n)</math>
where <math>\varphi</math> is Euler's totient function. The first few sparsely totient numbers are:
2, 6, 12, 18, 30, 42, 60, 66, 90, 120, 126, 150, 210, 240, 270, 330, 420, 462, 510, 630, 660, 690, 840, 870, 1050, 1260, 1320, 1470, 1680, 1890, 2310, 2730, 2940, 3150, 3570, 3990, 4620, 4830, 5460, 5610, 5670, 6090, 6930, 7140, 7350, 8190, 9240, 9660, 9870, ... .
The concept was introduced by David Masser and Peter Man-Kit Shiu in 1986. As they showed, every primorial is sparsely totient.
Properties
- If P(n) is the largest prime factor of n, then <math>\liminf P(n)/\log n=1</math>.
- <math>P(n)\ll \log^\delta n</math> holds for an exponent <math>\delta=37/20</math>.
- It is conjectured that <math>\limsup P(n) / \log n = 2</math>.
- They are always even because if x is odd, then 2x also has the same Totient function, trivially failing the condition that all numbers more than it has more value of Totient function than it.