21409581 has 8 divisors (see below), whose sum is σ = 29153664. Its totient is φ = 13969280.

The previous prime is 21409559. The next prime is 21409603. The reversal of 21409581 is 18590412.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21409559) and next prime (21409603).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21409581 - 2¹⁰ = 21408557 is a prime.

It is a super-2 number, since 2×21409581² = 916740317191122, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21409501) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 75780 + ... + 76061.

It is an arithmetic number, because the mean of its divisors is an integer number (3644208).

Almost surely, 2^21409581 is an apocalyptic number.

It is an amenable number.

21409581 is a deficient number, since it is larger than the sum of its proper divisors (7744083).

21409581 is a wasteful number, since it uses less digits than its factorization.

21409581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 151891.

The product of its (nonzero) digits is 2880, while the sum is 30.

The square root of 21409581 is about 4627.0488434854. The cubic root of 21409581 is about 277.6745367386.

Adding to 21409581 its reverse (18590412), we get a palindrome (39999993).

The spelling of 21409581 in words is "twenty-one million, four hundred nine thousand, five hundred eighty-one".