21081660 has 24 divisors (see below), whose sum is σ = 59028816. Its totient is φ = 5621760.

The previous prime is 21081647. The next prime is 21081673. The reversal of 21081660 is 6618012.

It is an interprime number because it is at equal distance from previous prime (21081647) and next prime (21081673).

It is a self number, because there is not a number n which added to its sum of digits gives 21081660.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 175621 + ... + 175740.

It is an arithmetic number, because the mean of its divisors is an integer number (2459534).

Almost surely, 2^21081660 is an apocalyptic number.

21081660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21081660 is an abundant number, since it is smaller than the sum of its proper divisors (37947156).

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

21081660 is a wasteful number, since it uses less digits than its factorization.

21081660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 351373 (or 351371 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 24.

The square root of 21081660 is about 4591.4768865802. The cubic root of 21081660 is about 276.2495642315.

Adding to 21081660 its reverse (6618012), we get a palindrome (27699672).

The spelling of 21081660 in words is "twenty-one million, eighty-one thousand, six hundred sixty".