21381641 has 4 divisors (see below), whose sum is σ = 21428484. Its totient is φ = 21334800.

The previous prime is 21381617. The next prime is 21381653. The reversal of 21381641 is 14618312.

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 10465225 + 10916416 = 3235^2 + 3304^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21381641 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21381641.

It is not an unprimeable number, because it can be changed into a prime (21381611) 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, 22730 + ... + 23651.

It is an arithmetic number, because the mean of its divisors is an integer number (5357121).

Almost surely, 2^21381641 is an apocalyptic number.

It is an amenable number.

21381641 is a deficient number, since it is larger than the sum of its proper divisors (46843).

21381641 is an equidigital number, since it uses as much as digits as its factorization.

21381641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46842.

The product of its digits is 1152, while the sum is 26.

The square root of 21381641 is about 4624.0286547555. The cubic root of 21381641 is about 277.5536935844.

Adding to 21381641 its reverse (14618312), we get a palindrome (35999953).

It can be divided in two parts, 21381 and 641, that added together give a palindrome (22022).

The spelling of 21381641 in words is "twenty-one million, three hundred eighty-one thousand, six hundred forty-one".