21031551 has 6 divisors (see below), whose sum is σ = 30378920. Its totient is φ = 14021028.

The previous prime is 21031531. The next prime is 21031559. The reversal of 21031551 is 15513012.

It is not a de Polignac number, because 21031551 - 2⁶ = 21031487 is a prime.

It is a super-2 number, since 2×21031551² = 884652274931202, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21031559) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1168411 + ... + 1168428.

Almost surely, 2^21031551 is an apocalyptic number.

21031551 is a deficient number, since it is larger than the sum of its proper divisors (9347369).

21031551 is a wasteful number, since it uses less digits than its factorization.

21031551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2336845 (or 2336842 counting only the distinct ones).

The product of its (nonzero) digits is 150, while the sum is 18.

The square root of 21031551 is about 4586.0168992275. The cubic root of 21031551 is about 276.0305180495.

Adding to 21031551 its reverse (15513012), we get a palindrome (36544563).

The spelling of 21031551 in words is "twenty-one million, thirty-one thousand, five hundred fifty-one".