21381577 has 8 divisors (see below), whose sum is σ = 24489792. Its totient is φ = 18286800.

The previous prime is 21381557. The next prime is 21381611. The reversal of 21381577 is 77518312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21381577 - 2¹⁵ = 21348809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21381527) 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, 327 + ... + 6547.

It is an arithmetic number, because the mean of its divisors is an integer number (3061224).

Almost surely, 2^21381577 is an apocalyptic number.

It is an amenable number.

21381577 is a deficient number, since it is larger than the sum of its proper divisors (3108215).

21381577 is an equidigital number, since it uses as much as digits as its factorization.

21381577 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6719.

The product of its digits is 11760, while the sum is 34.

The square root of 21381577 is about 4624.0217343780. The cubic root of 21381577 is about 277.5534166575.

Adding to 21381577 its reverse (77518312), we get a palindrome (98899889).

The spelling of 21381577 in words is "twenty-one million, three hundred eighty-one thousand, five hundred seventy-seven".