21381730 has 16 divisors (see below), whose sum is σ = 38659320. Its totient is φ = 8514432.

The previous prime is 21381653. The next prime is 21381739. The reversal of 21381730 is 3718312.

It can be written as a sum of positive squares in 4 ways, for example, as 21261321 + 120409 = 4611^2 + 347^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21381695 and 21381704.

It is not an unprimeable number, because it can be changed into a prime (21381739) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2379 + ... + 6958.

Almost surely, 2^21381730 is an apocalyptic number.

21381730 is a deficient number, since it is larger than the sum of its proper divisors (17277590).

21381730 is a wasteful number, since it uses less digits than its factorization.

21381730 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9573.

The product of its (nonzero) digits is 1008, while the sum is 25.

The square root of 21381730 is about 4624.0382783883. The cubic root of 21381730 is about 277.5540786849.

The spelling of 21381730 in words is "twenty-one million, three hundred eighty-one thousand, seven hundred thirty".