21005560 has 32 divisors (see below), whose sum is σ = 47480400. Its totient is φ = 8363520.

The previous prime is 21005539. The next prime is 21005561. The reversal of 21005560 is 6550012.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005561) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8551 + ... + 10729.

Almost surely, 2^21005560 is an apocalyptic number.

21005560 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21005560 is an abundant number, since it is smaller than the sum of its proper divisors (26474840).

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

21005560 is a wasteful number, since it uses less digits than its factorization.

21005560 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2431 (or 2427 counting only the distinct ones).

The product of its (nonzero) digits is 300, while the sum is 19.

The square root of 21005560 is about 4583.1823005418. The cubic root of 21005560 is about 275.9167640902.

Adding to 21005560 its reverse (6550012), we get a palindrome (27555572).

The spelling of 21005560 in words is "twenty-one million, five thousand, five hundred sixty".