561

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Summary

Factorization

561 is a square-free number with prime factors 3, 11, and 17. The prime factorization is:

$\!561=3*11*17$

Properties and families

Property or family	Parameter values	First few numbers satisfying the property	Proof of satisfaction/membership/containment
Carmichael number (also called absolute pseudoprime)	first Carmichael number	561, 1105, 1729, 2465, 2821, 6601, [SHOW MORE] 8911, 10585, 15841, 29341, 41041, 46657, 52633, 62745, 63973, 75361, 101101, 115921, 126217, 162401, 172081, 188461, 252601, 278545, 294409, 314821, 334153, 340561, 399001, 410041, 449065, 488881, 512461 View list on OEIS	The universal exponent is $\operatorname {lcm} \{3-1,11-1,17-1\}=80$ which divides $561-1=560$
Poulet number (Fermat pseudoprime to base 2)	second Poulet number	341, 561, 645, 1105, 1387, 1729, 1905, 2047, [SHOW MORE] 2465, 2701, 2821, 3277, 4033, 4369, 4371, 4681, 5461, 6601, 7957, 8321, 8481, 8911, 10261, 10585, 11305, 12801, 13741, 13747, 13981, 14491, 15709, 15841, 16705, 18705, 18721, 19951, 23001, 23377, 25761, 29341 View list on OEIS	follows from its being an odd Carmichael number.

Arithmetic functions

Function	Value	Explanation
Euler totient function	320	The Euler totient function is $(3-1)(11-1)(17-1)=(2)(10)(16)=320$.
universal exponent	80	The universal exponent is the least common multiple of $\{3-1,11-1,17-1\}$, which is $\operatorname {lcm} \{2,10,16\}$ and equals 80. Note that 561 is a Carmichael number precisely because the universal exponent divides 561 - 1 = 560.
Mobius function	-1	The number is a square-free number and it has an odd number of prime divisors (3 prime divisors).
divisor count function	8	$(1+1)(1+1)(1+1)$ where the first 1s in each sum denote the multiplicities of the prime divisors.
largest prime divisor	17
largest prime power divisor	17