21006972 has 96 divisors (see below), whose sum is σ = 64010240. Its totient is φ = 5832000.

The previous prime is 21006971. The next prime is 21006977. The reversal of 21006972 is 27960012.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006971) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 27597 + ... + 28347.

Almost surely, 2^21006972 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 21006972, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32005120).

21006972 is an abundant number, since it is smaller than the sum of its proper divisors (43003268).

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

21006972 is a wasteful number, since it uses less digits than its factorization.

21006972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 808 (or 800 counting only the distinct ones).

The product of its (nonzero) digits is 1512, while the sum is 27.

The square root of 21006972 is about 4583.3363393930. The cubic root of 21006972 is about 275.9229463541.

Adding to 21006972 its reverse (27960012), we get a palindrome (48966984).

The spelling of 21006972 in words is "twenty-one million, six thousand, nine hundred seventy-two".