21017631 has 4 divisors (see below), whose sum is σ = 28023512. Its totient is φ = 14011752.

The previous prime is 21017621. The next prime is 21017641. The reversal of 21017631 is 13671012.

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

It is an interprime number because it is at equal distance from previous prime (21017621) and next prime (21017641).

It is not a de Polignac number, because 21017631 - 2⁵ = 21017599 is a prime.

It is a super-2 number, since 2×21017631² = 883481625704322, 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 = 21017598 and 21017607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21017621) 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 3 ways as a sum of consecutive naturals, for example, 3502936 + ... + 3502941.

It is an arithmetic number, because the mean of its divisors is an integer number (7005878).

Almost surely, 2^21017631 is an apocalyptic number.

21017631 is a deficient number, since it is larger than the sum of its proper divisors (7005881).

21017631 is an equidigital number, since it uses as much as digits as its factorization.

21017631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7005880.

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 21017631 is about 4584.4989911658. The cubic root of 21017631 is about 275.9696065040.

Adding to 21017631 its reverse (13671012), we get a palindrome (34688643).

The spelling of 21017631 in words is "twenty-one million, seventeen thousand, six hundred thirty-one".