21511551 has 16 divisors (see below), whose sum is σ = 29742080. Its totient is φ = 13815360.

The previous prime is 21511549. The next prime is 21511561. The reversal of 21511551 is 15511512.

It is not a de Polignac number, because 21511551 - 2¹ = 21511549 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21511531) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 28740 + ... + 29478.

It is an arithmetic number, because the mean of its divisors is an integer number (1858880).

Almost surely, 2^21511551 is an apocalyptic number.

21511551 is a deficient number, since it is larger than the sum of its proper divisors (8230529).

21511551 is a wasteful number, since it uses less digits than its factorization.

21511551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1086.

The product of its digits is 250, while the sum is 21.

The square root of 21511551 is about 4638.0546568578. The cubic root of 21511551 is about 278.1146767367.

The spelling of 21511551 in words is "twenty-one million, five hundred eleven thousand, five hundred fifty-one".