21531651 has 4 divisors (see below), whose sum is σ = 28708872. Its totient is φ = 14354432.

The previous prime is 21531649. The next prime is 21531667. The reversal of 21531651 is 15613512.

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 21531651 - 2¹ = 21531649 is a prime.

It is a super-2 number, since 2×21531651² = 927223989571602, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21531641) 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, 3588606 + ... + 3588611.

It is an arithmetic number, because the mean of its divisors is an integer number (7177218).

Almost surely, 2^21531651 is an apocalyptic number.

21531651 is a deficient number, since it is larger than the sum of its proper divisors (7177221).

21531651 is an equidigital number, since it uses as much as digits as its factorization.

21531651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7177220.

The product of its digits is 900, while the sum is 24.

The square root of 21531651 is about 4640.2210076676. The cubic root of 21531651 is about 278.2012715280.

The spelling of 21531651 in words is "twenty-one million, five hundred thirty-one thousand, six hundred fifty-one".