21157987449 has 16 divisors (see below), whose sum is σ = 29976419520. Its totient is φ = 13228346880.

The previous prime is 21157987441. The next prime is 21157987457. The reversal of 21157987449 is 94478975112.

It is an interprime number because it is at equal distance from previous prime (21157987441) and next prime (21157987457).

It is not a de Polignac number, because 21157987449 - 2³ = 21157987441 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21157987441) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 723859 + ... + 752520.

It is an arithmetic number, because the mean of its divisors is an integer number (1873526220).

Almost surely, 2^21157987449 is an apocalyptic number.

It is an amenable number.

21157987449 is a deficient number, since it is larger than the sum of its proper divisors (8818432071).

21157987449 is a wasteful number, since it uses less digits than its factorization.

21157987449 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1476680.

The product of its digits is 5080320, while the sum is 57.

The spelling of 21157987449 in words is "twenty-one billion, one hundred fifty-seven million, nine hundred eighty-seven thousand, four hundred forty-nine".