21005550 has 36 divisors (see below), whose sum is σ = 56436120. Its totient is φ = 5601360.

The previous prime is 21005539. The next prime is 21005561. The reversal of 21005550 is 5550012.

It is an interprime number because it is at equal distance from previous prime (21005539) and next prime (21005561).

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 22890 + ... + 23789.

It is an arithmetic number, because the mean of its divisors is an integer number (1567670).

Almost surely, 2^21005550 is an apocalyptic number.

21005550 is an abundant number, since it is smaller than the sum of its proper divisors (35430570).

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

21005550 is a wasteful number, since it uses less digits than its factorization.

21005550 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46697 (or 46689 counting only the distinct ones).

The product of its (nonzero) digits is 250, while the sum is 18.

The square root of 21005550 is about 4583.1812095967. The cubic root of 21005550 is about 275.9167203055.

Adding to 21005550 its reverse (5550012), we get a palindrome (26555562).

The spelling of 21005550 in words is "twenty-one million, five thousand, five hundred fifty".