21501768 has 64 divisors (see below), whose sum is σ = 57585600. Its totient is φ = 6670080.

The previous prime is 21501737. The next prime is 21501811. The reversal of 21501768 is 86710512.

It is a Cunningham number, because it is equal to 4637²-1.

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, 27430 + ... + 28202.

It is an arithmetic number, because the mean of its divisors is an integer number (899775).

Almost surely, 2^21501768 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21501768, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28792800).

21501768 is an abundant number, since it is smaller than the sum of its proper divisors (36083832).

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

21501768 is a wasteful number, since it uses less digits than its factorization.

21501768 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 862 (or 858 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 30.

The square root of 21501768 is about 4636.9998921717. Note that the first 3 decimals coincide. The cubic root of 21501768 is about 278.0725101128.

The spelling of 21501768 in words is "twenty-one million, five hundred one thousand, seven hundred sixty-eight".