21651877 has 4 divisors (see below), whose sum is σ = 23317420. Its totient is φ = 19986336.

The previous prime is 21651859. The next prime is 21651881. The reversal of 21651877 is 77815612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8300161 + 13351716 = 2881^2 + 3654^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651877 - 2¹⁵ = 21619109 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651277) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 832752 + ... + 832777.

It is an arithmetic number, because the mean of its divisors is an integer number (5829355).

Almost surely, 2^21651877 is an apocalyptic number.

It is an amenable number.

21651877 is a deficient number, since it is larger than the sum of its proper divisors (1665543).

21651877 is a wasteful number, since it uses less digits than its factorization.

21651877 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1665542.

The product of its digits is 23520, while the sum is 37.

The square root of 21651877 is about 4653.1577450157. The cubic root of 21651877 is about 278.7181070444.

The spelling of 21651877 in words is "twenty-one million, six hundred fifty-one thousand, eight hundred seventy-seven".