21003666553 has 4 divisors (see below), whose sum is σ = 21085393140. Its totient is φ = 20921939968.

The previous prime is 21003666511. The next prime is 21003666557. The reversal of 21003666553 is 35566630012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13133847609 + 7869818944 = 114603^2 + 88712^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003666553 - 2⁹ = 21003666041 is a prime.

It is a super-2 number, since 2×21003666553² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21003666557) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 40862908 + ... + 40863421.

It is an arithmetic number, because the mean of its divisors is an integer number (5271348285).

Almost surely, 2^21003666553 is an apocalyptic number.

It is an amenable number.

21003666553 is a deficient number, since it is larger than the sum of its proper divisors (81726587).

21003666553 is an equidigital number, since it uses as much as digits as its factorization.

21003666553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81726586.

The product of its (nonzero) digits is 97200, while the sum is 37.

The spelling of 21003666553 in words is "twenty-one billion, three million, six hundred sixty-six thousand, five hundred fifty-three".