21287660 has 12 divisors (see below), whose sum is σ = 44704128. Its totient is φ = 8515056.

The previous prime is 21287659. The next prime is 21287681. The reversal of 21287660 is 6678212.

It is a super-3 number, since 3×21287660³ (a number of 23 digits) contains 333 as substring.

It is a hoax number, since the sum of its digits (32) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 532172 + ... + 532211.

It is an arithmetic number, because the mean of its divisors is an integer number (3725344).

Almost surely, 2^21287660 is an apocalyptic number.

21287660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21287660 is an abundant number, since it is smaller than the sum of its proper divisors (23416468).

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

21287660 is a wasteful number, since it uses less digits than its factorization.

21287660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1064392 (or 1064390 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 32.

The square root of 21287660 is about 4613.8552209622. The cubic root of 21287660 is about 277.1464425693.

The spelling of 21287660 in words is "twenty-one million, two hundred eighty-seven thousand, six hundred sixty".