21572556 has 24 divisors (see below), whose sum is σ = 50723904. Its totient is φ = 7135440.

The previous prime is 21572539. The next prime is 21572557. The reversal of 21572556 is 65527512.

It is not an unprimeable number, because it can be changed into a prime (21572557) 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, 5290 + ... + 8433.

It is an arithmetic number, because the mean of its divisors is an integer number (2113496).

Almost surely, 2^21572556 is an apocalyptic number.

It is an amenable number.

21572556 is an abundant number, since it is smaller than the sum of its proper divisors (29151348).

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

21572556 is a wasteful number, since it uses less digits than its factorization.

21572556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13861 (or 13859 counting only the distinct ones).

The product of its digits is 21000, while the sum is 33.

The square root of 21572556 is about 4644.6265727182. The cubic root of 21572556 is about 278.3773320988.

It can be divided in two parts, 215 and 72556, that added together give a triangular number (72771 = T₃₈₁).

The spelling of 21572556 in words is "twenty-one million, five hundred seventy-two thousand, five hundred fifty-six".