21356783680 has 56 divisors (see below), whose sum is σ = 51136951320. Its totient is φ = 8495493120.

The previous prime is 21356783671. The next prime is 21356783711. The reversal of 21356783680 is 8638765312.

It can be written as a sum of positive squares in 4 ways, for example, as 1729894464 + 19626889216 = 41592^2 + 140096^2 .

It is a super-2 number, since 2×21356783680² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 126445 + ... + 242284.

It is an arithmetic number, because the mean of its divisors is an integer number (913159845).

Almost surely, 2^21356783680 is an apocalyptic number.

21356783680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21356783680 is an abundant number, since it is smaller than the sum of its proper divisors (29780167640).

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

21356783680 is a wasteful number, since it uses less digits than its factorization.

21356783680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 368927 (or 368917 counting only the distinct ones).

The product of its (nonzero) digits is 1451520, while the sum is 49.

The spelling of 21356783680 in words is "twenty-one billion, three hundred fifty-six million, seven hundred eighty-three thousand, six hundred eighty".