21002553 has 24 divisors (see below), whose sum is σ = 35642880. Its totient is φ = 11748960.

The previous prime is 21002549. The next prime is 21002563. The reversal of 21002553 is 35520012.

It is a happy number.

It is not a de Polignac number, because 21002553 - 2² = 21002549 is a prime.

It is a super-2 number, since 2×21002553² = 882214465035618, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21002503) by changing a digit.

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 23 ways as a sum of consecutive naturals, for example, 6873 + ... + 9446.

It is an arithmetic number, because the mean of its divisors is an integer number (1485120).

Almost surely, 2^21002553 is an apocalyptic number.

It is an amenable number.

21002553 is a deficient number, since it is larger than the sum of its proper divisors (14640327).

21002553 is a wasteful number, since it uses less digits than its factorization.

21002553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16349 (or 16346 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 18.

The square root of 21002553 is about 4582.8542416272. The cubic root of 21002553 is about 275.9035973969.

Adding to 21002553 its reverse (35520012), we get a palindrome (56522565).

The spelling of 21002553 in words is "twenty-one million, two thousand, five hundred fifty-three".