21540006 has 96 divisors (see below), whose sum is σ = 52835328. Its totient is φ = 6557760.

The previous prime is 21539993. The next prime is 21540017. The reversal of 21540006 is 60004512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 458275 + ... + 458321.

It is an arithmetic number, because the mean of its divisors is an integer number (550368).

Almost surely, 2^21540006 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21540006, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26417664).

21540006 is an abundant number, since it is smaller than the sum of its proper divisors (31295322).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21540006 is a wasteful number, since it uses less digits than its factorization.

21540006 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 128 (or 116 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21540006 is about 4641.1212007445. The cubic root of 21540006 is about 278.2372506709.

Subtracting from 21540006 its product of nonzero digits (240), we obtain a triangular number (21539766 = T₆₅₆₃).

Adding to 21540006 its reverse (60004512), we get a palindrome (81544518).

The spelling of 21540006 in words is "twenty-one million, five hundred forty thousand, six".