21387861 has 64 divisors (see below), whose sum is σ = 37601280. Its totient is φ = 11880000.

The previous prime is 21387851. The next prime is 21387893. The reversal of 21387861 is 16878312.

It is not a de Polignac number, because 21387861 - 2⁷ = 21387733 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21387811) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 211711 + ... + 211811.

It is an arithmetic number, because the mean of its divisors is an integer number (587520).

Almost surely, 2^21387861 is an apocalyptic number.

It is an amenable number.

21387861 is a deficient number, since it is larger than the sum of its proper divisors (16213419).

21387861 is a wasteful number, since it uses less digits than its factorization.

21387861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 175 (or 169 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 21387861 is about 4624.7011795358. The cubic root of 21387861 is about 277.5806047804.

It can be divided in two parts, 2138 and 7861, that added together give a palindrome (9999).

The spelling of 21387861 in words is "twenty-one million, three hundred eighty-seven thousand, eight hundred sixty-one".