21561012 has 48 divisors (see below), whose sum is σ = 60984000. Its totient is φ = 6533280.

The previous prime is 21561011. The next prime is 21561013. The reversal of 21561012 is 21016512.

It is an interprime number because it is at equal distance from previous prime (21561011) and next prime (21561013).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561011) 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, 7887 + ... + 10262.

It is an arithmetic number, because the mean of its divisors is an integer number (1270500).

Almost surely, 2^21561012 is an apocalyptic number.

21561012 is a gapful number since it is divisible by the number (22) formed by its first and last digit.

It is an amenable number.

21561012 is an abundant number, since it is smaller than the sum of its proper divisors (39422988).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21561012 is a wasteful number, since it uses less digits than its factorization.

21561012 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18173 (or 18165 counting only the distinct ones).

The product of its (nonzero) digits is 120, while the sum is 18.

The square root of 21561012 is about 4643.3836800333. The cubic root of 21561012 is about 278.3276677426.

Adding to 21561012 its reverse (21016512), we get a palindrome (42577524).

The spelling of 21561012 in words is "twenty-one million, five hundred sixty-one thousand, twelve".