21191556500 has 24 divisors (see below), whose sum is σ = 46282360488. Its totient is φ = 8476622400.

The previous prime is 21191556497. The next prime is 21191556521. The reversal of 21191556500 is 565519112.

It can be written as a sum of positive squares in 4 ways, for example, as 447491716 + 20744064784 = 21154^2 + 144028^2 .

It is a congruent number.

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, 21191057 + ... + 21192056.

It is an arithmetic number, because the mean of its divisors is an integer number (1928431687).

Almost surely, 2^21191556500 is an apocalyptic number.

21191556500 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21191556500 is an abundant number, since it is smaller than the sum of its proper divisors (25090803988).

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

21191556500 is a wasteful number, since it uses less digits than its factorization.

21191556500 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42383132 (or 42383120 counting only the distinct ones).

The product of its (nonzero) digits is 13500, while the sum is 35.

The spelling of 21191556500 in words is "twenty-one billion, one hundred ninety-one million, five hundred fifty-six thousand, five hundred".