21661860 has 96 divisors (see below), whose sum is σ = 69092352. Its totient is φ = 5019520.

The previous prime is 21661853. The next prime is 21661873. The reversal of 21661860 is 6816612.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 14467 + ... + 15893.

It is an arithmetic number, because the mean of its divisors is an integer number (719712).

Almost surely, 2^21661860 is an apocalyptic number.

21661860 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21661860, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34546176).

21661860 is an abundant number, since it is smaller than the sum of its proper divisors (47430492).

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

21661860 is a wasteful number, since it uses less digits than its factorization.

21661860 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1473 (or 1471 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 21661860 is about 4654.2303337931. The cubic root of 21661860 is about 278.7609365158.

The spelling of 21661860 in words is "twenty-one million, six hundred sixty-one thousand, eight hundred sixty".