21512021 has 8 divisors (see below), whose sum is σ = 22852224. Its totient is φ = 20180160.

The previous prime is 21512017. The next prime is 21512027. The reversal of 21512021 is 12021512.

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 21512021 - 2² = 21512017 is a prime.

It is a super-3 number, since 3×21512021³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21511987 and 21512005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21512027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3716 + ... + 7538.

It is an arithmetic number, because the mean of its divisors is an integer number (2856528).

Almost surely, 2^21512021 is an apocalyptic number.

It is an amenable number.

21512021 is a deficient number, since it is larger than the sum of its proper divisors (1340203).

21512021 is a wasteful number, since it uses less digits than its factorization.

21512021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4171.

The product of its (nonzero) digits is 40, while the sum is 14.

The square root of 21512021 is about 4638.1053243755. The cubic root of 21512021 is about 278.1167022058.

Adding to 21512021 its reverse (12021512), we get a palindrome (33533533).

The spelling of 21512021 in words is "twenty-one million, five hundred twelve thousand, twenty-one".