21508740 has 240 divisors, whose sum is σ = 79035264. Its totient is φ = 4838400.

The previous prime is 21508717. The next prime is 21508763. The reversal of 21508740 is 4780512.

It is an interprime number because it is at equal distance from previous prime (21508717) and next prime (21508763).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 302905 + ... + 302975.

Almost surely, 2^21508740 is an apocalyptic number.

21508740 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21508740, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39517632).

21508740 is an abundant number, since it is smaller than the sum of its proper divisors (57526524).

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

21508740 is a wasteful number, since it uses less digits than its factorization.

21508740 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120 (or 109 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 27.

The square root of 21508740 is about 4637.7516104250. The cubic root of 21508740 is about 278.1025620917.

The spelling of 21508740 in words is "twenty-one million, five hundred eight thousand, seven hundred forty".