21505597990 has 16 divisors (see below), whose sum is σ = 38713438080. Its totient is φ = 8601492160.

The previous prime is 21505597973. The next prime is 21505597991. The reversal of 21505597990 is 9979550512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505597991) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 36075 + ... + 210505.

It is an arithmetic number, because the mean of its divisors is an integer number (2419589880).

Almost surely, 2^21505597990 is an apocalyptic number.

21505597990 is a deficient number, since it is larger than the sum of its proper divisors (17207840090).

21505597990 is a wasteful number, since it uses less digits than its factorization.

21505597990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 186767.

The product of its (nonzero) digits is 1275750, while the sum is 52.

The spelling of 21505597990 in words is "twenty-one billion, five hundred five million, five hundred ninety-seven thousand, nine hundred ninety".