21406660 has 24 divisors (see below), whose sum is σ = 49041216. Its totient is φ = 7784160.

The previous prime is 21406643. The next prime is 21406663. The reversal of 21406660 is 6660412.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21406663) 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 7 ways as a sum of consecutive naturals, for example, 48432 + ... + 48871.

It is an arithmetic number, because the mean of its divisors is an integer number (2043384).

Almost surely, 2^21406660 is an apocalyptic number.

21406660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21406660 is an abundant number, since it is smaller than the sum of its proper divisors (27634556).

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

21406660 is a wasteful number, since it uses less digits than its factorization.

21406660 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 97323 (or 97321 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 21406660 is about 4626.7331887629. The cubic root of 21406660 is about 277.6619080591.

The spelling of 21406660 in words is "twenty-one million, four hundred six thousand, six hundred sixty".