21371581 has 16 divisors (see below), whose sum is σ = 26748288. Its totient is φ = 16588800.

The previous prime is 21371569. The next prime is 21371591. The reversal of 21371581 is 18517312.

It is a 7-Lehmer number, since φ(21371581) divides (21371581-1)⁷.

It is a cyclic number.

It is not a de Polignac number, because 21371581 - 2⁹ = 21371069 is a prime.

It is a super-2 number, since 2×21371581² = 913488948879122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21371551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 33021 + ... + 33661.

It is an arithmetic number, because the mean of its divisors is an integer number (1671768).

Almost surely, 2^21371581 is an apocalyptic number.

It is an amenable number.

21371581 is a deficient number, since it is larger than the sum of its proper divisors (5376707).

21371581 is a wasteful number, since it uses less digits than its factorization.

21371581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1092.

The product of its digits is 1680, while the sum is 28.

The square root of 21371581 is about 4622.9407307470. The cubic root of 21371581 is about 277.5101573535.

Adding to 21371581 its reverse (18517312), we get a palindrome (39888893).

It can be divided in two parts, 21371 and 581, that added together give a cube (21952 = 28³).

The spelling of 21371581 in words is "twenty-one million, three hundred seventy-one thousand, five hundred eighty-one".