21381761 has 4 divisors (see below), whose sum is σ = 21470724. Its totient is φ = 21292800.

The previous prime is 21381749. The next prime is 21381769. The reversal of 21381761 is 16718312.

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 11771761 + 9610000 = 3431^2 + 3100^2 .

It is a cyclic number.

It is not a de Polignac number, because 21381761 - 2¹⁸ = 21119617 is a prime.

It is a super-2 number, since 2×21381761² = 914359406922242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21381769) 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, 44120 + ... + 44601.

It is an arithmetic number, because the mean of its divisors is an integer number (5367681).

Almost surely, 2^21381761 is an apocalyptic number.

It is an amenable number.

21381761 is a deficient number, since it is larger than the sum of its proper divisors (88963).

21381761 is an equidigital number, since it uses as much as digits as its factorization.

21381761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 88962.

The product of its digits is 2016, while the sum is 29.

The square root of 21381761 is about 4624.0416304354. The cubic root of 21381761 is about 277.5542128208.

The spelling of 21381761 in words is "twenty-one million, three hundred eighty-one thousand, seven hundred sixty-one".