21545523666 has 64 divisors (see below), whose sum is σ = 48937046400. Its totient is φ = 7024449600.

The previous prime is 21545523661. The next prime is 21545523691. The reversal of 21545523666 is 66632554512.

It is not an unprimeable number, because it can be changed into a prime (21545523661) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 571356 + ... + 607896.

It is an arithmetic number, because the mean of its divisors is an integer number (764641350).

Almost surely, 2^21545523666 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21545523666, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24468523200).

21545523666 is an abundant number, since it is smaller than the sum of its proper divisors (27391522734).

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

21545523666 is a wasteful number, since it uses less digits than its factorization.

21545523666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36792 (or 36786 counting only the distinct ones).

The product of its digits is 1296000, while the sum is 45.

It can be divided in two parts, 215455 and 23666, that added together give a square (239121 = 489²).

The spelling of 21545523666 in words is "twenty-one billion, five hundred forty-five million, five hundred twenty-three thousand, six hundred sixty-six".