21521989 has 8 divisors (see below), whose sum is σ = 21830040. Its totient is φ = 21216000.

The previous prime is 21521987. The next prime is 21521999. The reversal of 21521989 is 98912512.

It can be written as a sum of positive squares in 4 ways, for example, as 11492100 + 10029889 = 3390^2 + 3167^2 .

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 21521989 - 2¹ = 21521987 is a prime.

It is a super-2 number, since 2×21521989² = 926392021032242, 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 (21521987) 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, 41049 + ... + 41569.

It is an arithmetic number, because the mean of its divisors is an integer number (2728755).

Almost surely, 2^21521989 is an apocalyptic number.

It is an amenable number.

21521989 is a deficient number, since it is larger than the sum of its proper divisors (308051).

21521989 is a wasteful number, since it uses less digits than its factorization.

21521989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1031.

The product of its digits is 12960, while the sum is 37.

The square root of 21521989 is about 4639.1797766416. The cubic root of 21521989 is about 278.1596524429.

The spelling of 21521989 in words is "twenty-one million, five hundred twenty-one thousand, nine hundred eighty-nine".