21147831 has 16 divisors (see below), whose sum is σ = 32178400. Its totient is φ = 13716864.

The previous prime is 21147829. The next prime is 21147839. The reversal of 21147831 is 13874112.

It is not a de Polignac number, because 21147831 - 2¹ = 21147829 is a prime.

It is a super-2 number, since 2×21147831² = 894461512009122, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21147795 and 21147804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21147839) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9586 + ... + 11583.

It is an arithmetic number, because the mean of its divisors is an integer number (2011150).

Almost surely, 2^21147831 is an apocalyptic number.

21147831 is a deficient number, since it is larger than the sum of its proper divisors (11030569).

21147831 is a wasteful number, since it uses less digits than its factorization.

21147831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21215 (or 21209 counting only the distinct ones).

The product of its digits is 1344, while the sum is 27.

The square root of 21147831 is about 4598.6770923821. The cubic root of 21147831 is about 276.5382925666.

The spelling of 21147831 in words is "twenty-one million, one hundred forty-seven thousand, eight hundred thirty-one".