21315631 has 8 divisors (see below), whose sum is σ = 22063104. Its totient is φ = 20571960.

The previous prime is 21315611. The next prime is 21315643. The reversal of 21315631 is 13651312.

It is a happy number.

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 21315631 - 2⁵ = 21315599 is a prime.

It is a super-2 number, since 2×21315631² = 908712249856322, which contains 22 as substring.

It is a Duffinian number.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21315611) 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, 14910 + ... + 16276.

It is an arithmetic number, because the mean of its divisors is an integer number (2757888).

Almost surely, 2^21315631 is an apocalyptic number.

21315631 is a deficient number, since it is larger than the sum of its proper divisors (747473).

21315631 is a wasteful number, since it uses less digits than its factorization.

21315631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1901.

The product of its digits is 540, while the sum is 22.

The square root of 21315631 is about 4616.8854220134. The cubic root of 21315631 is about 277.2677753092.

Adding to 21315631 its reverse (13651312), we get a palindrome (34966943).

The spelling of 21315631 in words is "twenty-one million, three hundred fifteen thousand, six hundred thirty-one".