21251506842 has 20 divisors (see below), whose sum is σ = 47619117546. Its totient is φ = 7083835560.

The previous prime is 21251506799. The next prime is 21251506867. The reversal of 21251506842 is 24860515212.

21251506842 is a `hidden beast` number, since 21 + 2 + 51 + 506 + 84 + 2 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21181600521 + 69906321 = 145539^2 + 8361^2 .

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a junction number, because it is equal to n+sod(n) for n = 21251506797 and 21251506806.

It is an unprimeable number.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 65590909 + ... + 65591232.

Almost surely, 2^21251506842 is an apocalyptic number.

21251506842 is an abundant number, since it is smaller than the sum of its proper divisors (26367610704).

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

21251506842 is a wasteful number, since it uses less digits than its factorization.

21251506842 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 131182155 (or 131182146 counting only the distinct ones).

The product of its (nonzero) digits is 38400, while the sum is 36.

The spelling of 21251506842 in words is "twenty-one billion, two hundred fifty-one million, five hundred six thousand, eight hundred forty-two".