21438551 has 4 divisors (see below), whose sum is σ = 21534912. Its totient is φ = 21342192.

The previous prime is 21438541. The next prime is 21438589. The reversal of 21438551 is 15583412.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21438551 is a prime.

It is a super-2 number, since 2×21438551² = 919222937959202, 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 (21438541) 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 3 ways as a sum of consecutive naturals, for example, 47846 + ... + 48291.

It is an arithmetic number, because the mean of its divisors is an integer number (5383728).

Almost surely, 2^21438551 is an apocalyptic number.

21438551 is a deficient number, since it is larger than the sum of its proper divisors (96361).

21438551 is an equidigital number, since it uses as much as digits as its factorization.

21438551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96360.

The product of its digits is 4800, while the sum is 29.

The square root of 21438551 is about 4630.1782903037. The cubic root of 21438551 is about 277.7997237713.

The spelling of 21438551 in words is "twenty-one million, four hundred thirty-eight thousand, five hundred fifty-one".