21612840 has 64 divisors (see below), whose sum is σ = 65145600. Its totient is φ = 5736192.

The previous prime is 21612839. The next prime is 21612841. The reversal of 21612840 is 4821612.

It is an interprime number because it is at equal distance from previous prime (21612839) and next prime (21612841).

It is a super-2 number, since 2×21612840² = 934229705731200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21612840.

It is not an unprimeable number, because it can be changed into a prime (21612841) 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, 46449 + ... + 46911.

It is an arithmetic number, because the mean of its divisors is an integer number (1017900).

Almost surely, 2^21612840 is an apocalyptic number.

21612840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21612840 is an abundant number, since it is smaller than the sum of its proper divisors (43532760).

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

21612840 is a wasteful number, since it uses less digits than its factorization.

21612840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 866 (or 862 counting only the distinct ones).

The product of its (nonzero) digits is 768, while the sum is 24.

The square root of 21612840 is about 4648.9611742840. The cubic root of 21612840 is about 278.5505024198.

The spelling of 21612840 in words is "twenty-one million, six hundred twelve thousand, eight hundred forty".