21537620 has 24 divisors (see below), whose sum is σ = 48708744. Its totient is φ = 7952256.

The previous prime is 21537613. The next prime is 21537629. The reversal of 21537620 is 2673512.

It can be written as a sum of positive squares in 4 ways, for example, as 1359556 + 20178064 = 1166^2 + 4492^2 .

It is a Harshad number since it is a multiple of its sum of digits (26).

It is a self number, because there is not a number n which added to its sum of digits gives 21537620.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21537629) 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, 41159 + ... + 41678.

It is an arithmetic number, because the mean of its divisors is an integer number (2029531).

Almost surely, 2^21537620 is an apocalyptic number.

21537620 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21537620 is an abundant number, since it is smaller than the sum of its proper divisors (27171124).

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

21537620 is a wasteful number, since it uses less digits than its factorization.

21537620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82859 (or 82857 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 26.

The square root of 21537620 is about 4640.8641436698. The cubic root of 21537620 is about 278.2269767865.

The spelling of 21537620 in words is "twenty-one million, five hundred thirty-seven thousand, six hundred twenty".