21289561720 has 256 divisors, whose sum is σ = 60131808000. Its totient is φ = 6616940544.

The previous prime is 21289561687. The next prime is 21289561747. The reversal of 21289561720 is 2716598212.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 19196526 + ... + 19197634.

It is an arithmetic number, because the mean of its divisors is an integer number (234889875).

Almost surely, 2^21289561720 is an apocalyptic number.

21289561720 is a gapful number since it is divisible by the number (20) 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 21289561720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30065904000).

21289561720 is an abundant number, since it is smaller than the sum of its proper divisors (38842246280).

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

21289561720 is a wasteful number, since it uses less digits than its factorization.

21289561720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1290 (or 1286 counting only the distinct ones).

The product of its (nonzero) digits is 120960, while the sum is 43.

The spelling of 21289561720 in words is "twenty-one billion, two hundred eighty-nine million, five hundred sixty-one thousand, seven hundred twenty".