21523551 has 8 divisors (see below), whose sum is σ = 32797824. Its totient is φ = 12299160.

The previous prime is 21523543. The next prime is 21523571. The reversal of 21523551 is 15532512.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21523551 - 2³ = 21523543 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21523511) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 512445 + ... + 512486.

It is an arithmetic number, because the mean of its divisors is an integer number (4099728).

Almost surely, 2^21523551 is an apocalyptic number.

21523551 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21523551 is a deficient number, since it is larger than the sum of its proper divisors (11274273).

21523551 is a wasteful number, since it uses less digits than its factorization.

21523551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1024941.

The product of its digits is 1500, while the sum is 24.

The square root of 21523551 is about 4639.3481223120. The cubic root of 21523551 is about 278.1663816051.

The spelling of 21523551 in words is "twenty-one million, five hundred twenty-three thousand, five hundred fifty-one".