21718516 has 6 divisors (see below), whose sum is σ = 38007410. Its totient is φ = 10859256.

The previous prime is 21718513. The next prime is 21718523. The reversal of 21718516 is 61581712.

It can be written as a sum of positive squares in only one way, i.e., 21715600 + 2916 = 4660^2 + 54^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21718513) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2714811 + ... + 2714818.

Almost surely, 2^21718516 is an apocalyptic number.

It is an amenable number.

21718516 is a deficient number, since it is larger than the sum of its proper divisors (16288894).

21718516 is a wasteful number, since it uses less digits than its factorization.

21718516 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5429633 (or 5429631 counting only the distinct ones).

The product of its digits is 3360, while the sum is 31.

The square root of 21718516 is about 4660.3128650338. The cubic root of 21718516 is about 279.0037554682.

The spelling of 21718516 in words is "twenty-one million, seven hundred eighteen thousand, five hundred sixteen".