21723409 has 2 divisors, whose sum is σ = 21723410. Its totient is φ = 21723408.

The previous prime is 21723397. The next prime is 21723419. The reversal of 21723409 is 90432712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18037009 + 3686400 = 4247^2 + 1920^2 .

It is a cyclic number.

It is not a de Polignac number, because 21723409 - 2¹³ = 21715217 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21723419) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10861704 + 10861705.

It is an arithmetic number, because the mean of its divisors is an integer number (10861705).

Almost surely, 2^21723409 is an apocalyptic number.

It is an amenable number.

21723409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21723409 is an equidigital number, since it uses as much as digits as its factorization.

21723409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 21723409 is about 4660.8378002243. The cubic root of 21723409 is about 279.0247062991.

The spelling of 21723409 in words is "twenty-one million, seven hundred twenty-three thousand, four hundred nine".