21409861 has 12 divisors (see below), whose sum is σ = 23940000. Its totient is φ = 19127240.

The previous prime is 21409847. The next prime is 21409867. The reversal of 21409861 is 16890412.

It is a happy number.

It is not a de Polignac number, because 21409861 - 2⁷ = 21409733 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21409867) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5640 + ... + 8638.

It is an arithmetic number, because the mean of its divisors is an integer number (1995000).

Almost surely, 2^21409861 is an apocalyptic number.

It is an amenable number.

21409861 is a deficient number, since it is larger than the sum of its proper divisors (2530139).

21409861 is a wasteful number, since it uses less digits than its factorization.

21409861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3080 (or 3069 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 31.

The square root of 21409861 is about 4627.0791002532. The cubic root of 21409861 is about 277.6757472329.

The spelling of 21409861 in words is "twenty-one million, four hundred nine thousand, eight hundred sixty-one".