21666137664 has 112 divisors (see below), whose sum is σ = 57747619328. Its totient is φ = 7169015808.

The previous prime is 21666137659. The next prime is 21666137671. The reversal of 21666137664 is 46673166612.

It is a Harshad number since it is a multiple of its sum of digits (48).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 24704394 + ... + 24705270.

It is an arithmetic number, because the mean of its divisors is an integer number (515603744).

Almost surely, 2^21666137664 is an apocalyptic number.

21666137664 is a gapful number since it is divisible by the number (24) 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 21666137664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28873809664).

21666137664 is an abundant number, since it is smaller than the sum of its proper divisors (36081481664).

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

21666137664 is a wasteful number, since it uses less digits than its factorization.

21666137664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1692 (or 1682 counting only the distinct ones).

The product of its digits is 1306368, while the sum is 48.

It can be divided in two parts, 21666 and 137664, that added together give a triangular number (159330 = T₅₆₄).

The spelling of 21666137664 in words is "twenty-one billion, six hundred sixty-six million, one hundred thirty-seven thousand, six hundred sixty-four".