21061660 has 12 divisors (see below), whose sum is σ = 44229528. Its totient is φ = 8424656.

The previous prime is 21061639. The next prime is 21061669. The reversal of 21061660 is 6616012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21061669) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 526522 + ... + 526561.

It is an arithmetic number, because the mean of its divisors is an integer number (3685794).

Almost surely, 2^21061660 is an apocalyptic number.

21061660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21061660 is an abundant number, since it is smaller than the sum of its proper divisors (23167868).

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

21061660 is a wasteful number, since it uses less digits than its factorization.

21061660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1053092 (or 1053090 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 22.

The square root of 21061660 is about 4589.2984213276. The cubic root of 21061660 is about 276.1621780172.

Adding to 21061660 its reverse (6616012), we get a palindrome (27677672).

The spelling of 21061660 in words is "twenty-one million, sixty-one thousand, six hundred sixty".