21638977 has 4 divisors (see below), whose sum is σ = 22911876. Its totient is φ = 20366080.

The previous prime is 21638971. The next prime is 21638987. The reversal of 21638977 is 77983612.

It is a happy number.

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 11296321 + 10342656 = 3361^2 + 3216^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21638977 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21638971) 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, 636424 + ... + 636457.

It is an arithmetic number, because the mean of its divisors is an integer number (5727969).

Almost surely, 2^21638977 is an apocalyptic number.

It is an amenable number.

21638977 is a deficient number, since it is larger than the sum of its proper divisors (1272899).

21638977 is a wasteful number, since it uses less digits than its factorization.

21638977 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1272898.

The product of its digits is 127008, while the sum is 43.

The square root of 21638977 is about 4651.7713830325. The cubic root of 21638977 is about 278.6627434399.

It can be divided in two parts, 216 and 38977, that added together give a palindrome (39193).

The spelling of 21638977 in words is "twenty-one million, six hundred thirty-eight thousand, nine hundred seventy-seven".