21198657640 has 24 divisors (see below), whose sum is σ = 47699051670. Its totient is φ = 8479094720.

The previous prime is 21198657631. The next prime is 21198657691. The reversal of 21198657640 is 4675689112.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 8532955876 + 12665701764 = 92374^2 + 112542^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 909330 + ... + 932350.

Almost surely, 2^21198657640 is an apocalyptic number.

21198657640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21198657640 is an abundant number, since it is smaller than the sum of its proper divisors (26500394030).

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

21198657640 is an frugal number, since it uses more digits than its factorization.

21198657640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46053 (or 23028 counting only the distinct ones).

The product of its (nonzero) digits is 725760, while the sum is 49.

The spelling of 21198657640 in words is "twenty-one billion, one hundred ninety-eight million, six hundred fifty-seven thousand, six hundred forty".