21139861 has 4 divisors (see below), whose sum is σ = 21821824. Its totient is φ = 20457900.

The previous prime is 21139841. The next prime is 21139901. The reversal of 21139861 is 16893112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21139861 - 2¹¹ = 21137813 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 681931 = 21139861 / (2 + 1 + 1 + 3 + 9 + 8 + 6 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21139831) 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, 340935 + ... + 340996.

It is an arithmetic number, because the mean of its divisors is an integer number (5455456).

Almost surely, 2^21139861 is an apocalyptic number.

It is an amenable number.

21139861 is a deficient number, since it is larger than the sum of its proper divisors (681963).

21139861 is an equidigital number, since it uses as much as digits as its factorization.

21139861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 681962.

The product of its digits is 2592, while the sum is 31.

The square root of 21139861 is about 4597.8104571633. The cubic root of 21139861 is about 276.5035484657.

It can be divided in two parts, 2 and 1139861, that multiplied together give a palindrome (2279722).

The spelling of 21139861 in words is "twenty-one million, one hundred thirty-nine thousand, eight hundred sixty-one".