21016861 has 4 divisors (see below), whose sum is σ = 21028572. Its totient is φ = 21005152.

The previous prime is 21016859. The next prime is 21016873. The reversal of 21016861 is 16861012.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 11902500 + 9114361 = 3450^2 + 3019^2 .

It is a cyclic number.

It is not a de Polignac number, because 21016861 - 2¹ = 21016859 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 (21017861) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2536 + ... + 6961.

It is an arithmetic number, because the mean of its divisors is an integer number (5257143).

Almost surely, 2^21016861 is an apocalyptic number.

It is an amenable number.

21016861 is a deficient number, since it is larger than the sum of its proper divisors (11711).

21016861 is an equidigital number, since it uses as much as digits as its factorization.

21016861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11710.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21016861 is about 4584.4150117545. The cubic root of 21016861 is about 275.9662363305.

Adding to 21016861 its reverse (16861012), we get a palindrome (37877873).

It can be divided in two parts, 210 and 16861, that added together give a palindrome (17071).

The spelling of 21016861 in words is "twenty-one million, sixteen thousand, eight hundred sixty-one".