21402640 has 40 divisors (see below), whose sum is σ = 56871360. Its totient is φ = 7337856.

The previous prime is 21402637. The next prime is 21402653. The reversal of 21402640 is 4620412.

It is a tau number, because it is divible by the number of its divisors (40).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18550 + ... + 19669.

It is an arithmetic number, because the mean of its divisors is an integer number (1421784).

Almost surely, 2^21402640 is an apocalyptic number.

21402640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21402640 is an abundant number, since it is smaller than the sum of its proper divisors (35468720).

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

21402640 is a wasteful number, since it uses less digits than its factorization.

21402640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38239 (or 38233 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 19.

The square root of 21402640 is about 4626.2987365712. The cubic root of 21402640 is about 277.6445260737.

The spelling of 21402640 in words is "twenty-one million, four hundred two thousand, six hundred forty".