21509681428 has 12 divisors (see below), whose sum is σ = 37643340532. Its totient is φ = 10754441280.

The previous prime is 21509681423. The next prime is 21509681441. The reversal of 21509681428 is 82418690512.

It can be written as a sum of positive squares in 2 ways, for example, as 15535628164 + 5974053264 = 124642^2 + 77292^2 .

It is a hoax number, since the sum of its digits (46) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21509681423) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 44488 + ... + 212128.

Almost surely, 2^21509681428 is an apocalyptic number.

It is an amenable number.

21509681428 is a deficient number, since it is larger than the sum of its proper divisors (16133659104).

21509681428 is a wasteful number, since it uses less digits than its factorization.

21509681428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 199722 (or 199720 counting only the distinct ones).

The product of its (nonzero) digits is 276480, while the sum is 46.

The spelling of 21509681428 in words is "twenty-one billion, five hundred nine million, six hundred eighty-one thousand, four hundred twenty-eight".