21506531 has 8 divisors (see below), whose sum is σ = 21930000. Its totient is φ = 21086208.

The previous prime is 21506519. The next prime is 21506533. The reversal of 21506531 is 13560512.

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 21506531 - 2¹⁰ = 21505507 is a prime.

It is a super-2 number, since 2×21506531² = 925061751307922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21506497 and 21506506.

It is not an unprimeable number, because it can be changed into a prime (21506533) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16595 + ... + 17843.

It is an arithmetic number, because the mean of its divisors is an integer number (2741250).

Almost surely, 2^21506531 is an apocalyptic number.

21506531 is a deficient number, since it is larger than the sum of its proper divisors (423469).

21506531 is a wasteful number, since it uses less digits than its factorization.

21506531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1573.

The product of its (nonzero) digits is 900, while the sum is 23.

The square root of 21506531 is about 4637.5134501153. The cubic root of 21506531 is about 278.0930411622.

The spelling of 21506531 in words is "twenty-one million, five hundred six thousand, five hundred thirty-one".