21521640 has 64 divisors (see below), whose sum is σ = 73791360. Its totient is φ = 4919040.

The previous prime is 21521627. The next prime is 21521653. The reversal of 21521640 is 4612512.

It is an interprime number because it is at equal distance from previous prime (21521627) and next prime (21521653).

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11971 + ... + 13650.

It is an arithmetic number, because the mean of its divisors is an integer number (1152990).

Almost surely, 2^21521640 is an apocalyptic number.

21521640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21521640 is an abundant number, since it is smaller than the sum of its proper divisors (52269720).

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

21521640 is a wasteful number, since it uses less digits than its factorization.

21521640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 25642 (or 25638 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 21521640 is about 4639.1421620813. The cubic root of 21521640 is about 278.1581488916.

The spelling of 21521640 in words is "twenty-one million, five hundred twenty-one thousand, six hundred forty".