21002506 has 16 divisors (see below), whose sum is σ = 36167040. Its totient is φ = 8960400.

The previous prime is 21002503. The next prime is 21002507. The reversal of 21002506 is 60520012.

It is a happy number.

It is a super-2 number, since 2×21002506² = 882210516560072, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21002506.

It is not an unprimeable number, because it can be changed into a prime (21002503) 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, 70 + ... + 6481.

It is an arithmetic number, because the mean of its divisors is an integer number (2260440).

Almost surely, 2^21002506 is an apocalyptic number.

21002506 is a deficient number, since it is larger than the sum of its proper divisors (15164534).

21002506 is a wasteful number, since it uses less digits than its factorization.

21002506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6789.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21002506 is about 4582.8491138156. The cubic root of 21002506 is about 275.9033915889.

Adding to 21002506 its reverse (60520012), we get a palindrome (81522518).

The spelling of 21002506 in words is "twenty-one million, two thousand, five hundred six".