21159781 has 8 divisors (see below), whose sum is σ = 22555584. Its totient is φ = 19780800.

The previous prime is 21159779. The next prime is 21159791. The reversal of 21159781 is 18795112.

It is a happy number.

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 21159781 - 2¹ = 21159779 is a prime.

It is a super-2 number, since 2×21159781² = 895472663935922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21159751) 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, 1555 + ... + 6688.

It is an arithmetic number, because the mean of its divisors is an integer number (2819448).

Almost surely, 2^21159781 is an apocalyptic number.

It is an amenable number.

21159781 is a deficient number, since it is larger than the sum of its proper divisors (1395803).

21159781 is a wasteful number, since it uses less digits than its factorization.

21159781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8411.

The product of its digits is 5040, while the sum is 34.

The square root of 21159781 is about 4599.9761955906. The cubic root of 21159781 is about 276.5903705684.

The spelling of 21159781 in words is "twenty-one million, one hundred fifty-nine thousand, seven hundred eighty-one".