21278640 has 40 divisors (see below), whose sum is σ = 65964528. Its totient is φ = 5674240.

The previous prime is 21278633. The next prime is 21278641. The reversal of 21278640 is 4687212.

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

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

It is a junction number, because it is equal to n+sod(n) for n = 21278598 and 21278607.

It is not an unprimeable number, because it can be changed into a prime (21278641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44091 + ... + 44570.

Almost surely, 2^21278640 is an apocalyptic number.

21278640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21278640 is an abundant number, since it is smaller than the sum of its proper divisors (44685888).

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

21278640 is a wasteful number, since it uses less digits than its factorization.

21278640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 88677 (or 88671 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 30.

The square root of 21278640 is about 4612.8776268182. The cubic root of 21278640 is about 277.1072929074.

The spelling of 21278640 in words is "twenty-one million, two hundred seventy-eight thousand, six hundred forty".