21206511660 has 24 divisors (see below), whose sum is σ = 59378232816. Its totient is φ = 5655069760.

The previous prime is 21206511649. The next prime is 21206511661. The reversal of 21206511660 is 6611560212.

It is a super-2 number, since 2×21206511660² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (21206511661) 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, 176720871 + ... + 176720990.

It is an arithmetic number, because the mean of its divisors is an integer number (2474093034).

Almost surely, 2^21206511660 is an apocalyptic number.

21206511660 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21206511660 is an abundant number, since it is smaller than the sum of its proper divisors (38171721156).

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

21206511660 is a wasteful number, since it uses less digits than its factorization.

21206511660 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 353441873 (or 353441871 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 30.

The spelling of 21206511660 in words is "twenty-one billion, two hundred six million, five hundred eleven thousand, six hundred sixty".