21212531 has 4 divisors (see below), whose sum is σ = 22329000. Its totient is φ = 20096064.

The previous prime is 21212519. The next prime is 21212537. The reversal of 21212531 is 13521212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21212531 - 2⁶ = 21212467 is a prime.

It is a super-2 number, since 2×21212531² = 899942942851922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21212537) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 558206 + ... + 558243.

It is an arithmetic number, because the mean of its divisors is an integer number (5582250).

Almost surely, 2^21212531 is an apocalyptic number.

21212531 is a deficient number, since it is larger than the sum of its proper divisors (1116469).

21212531 is a wasteful number, since it uses less digits than its factorization.

21212531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1116468.

The product of its digits is 120, while the sum is 17.

The square root of 21212531 is about 4605.7063519074. The cubic root of 21212531 is about 276.8200206250.

Adding to 21212531 its reverse (13521212), we get a palindrome (34733743).

The spelling of 21212531 in words is "twenty-one million, two hundred twelve thousand, five hundred thirty-one".