21311550 has 72 divisors (see below), whose sum is σ = 61678344. Its totient is φ = 5244480.

The previous prime is 21311527. The next prime is 21311599. The reversal of 21311550 is 5511312.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

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 35 ways as a sum of consecutive naturals, for example, 4029 + ... + 7671.

Almost surely, 2^21311550 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21311550, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30839172).

21311550 is an abundant number, since it is smaller than the sum of its proper divisors (40366794).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21311550 is a wasteful number, since it uses less digits than its factorization.

21311550 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3674 (or 3666 counting only the distinct ones).

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

The square root of 21311550 is about 4616.4434362396. The cubic root of 21311550 is about 277.2500793437.

Adding to 21311550 its reverse (5511312), we get a palindrome (26822862).

The spelling of 21311550 in words is "twenty-one million, three hundred eleven thousand, five hundred fifty".