21081672 has 24 divisors (see below), whose sum is σ = 57096390. Its totient is φ = 7027200.

The previous prime is 21081647. The next prime is 21081673. The reversal of 21081672 is 27618012.

It can be written as a sum of positive squares in only one way, i.e., 15634116 + 5447556 = 3954^2 + 2334^2 .

It is a tau number, because it is divible by the number of its divisors (24).

It is a hoax number, since the sum of its digits (27) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21081673) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 146329 + ... + 146472.

Almost surely, 2^21081672 is an apocalyptic number.

It is an amenable number.

21081672 is an abundant number, since it is smaller than the sum of its proper divisors (36014718).

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

21081672 is a wasteful number, since it uses less digits than its factorization.

21081672 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 292813 (or 292806 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21081672 is about 4591.4781933491. The cubic root of 21081672 is about 276.2496166467.

Adding to 21081672 its reverse (27618012), we get a palindrome (48699684).

The spelling of 21081672 in words is "twenty-one million, eighty-one thousand, six hundred seventy-two".