21256515078 has 16 divisors (see below), whose sum is σ = 42525119280. Its totient is φ = 7083490176.

The previous prime is 21256515047. The next prime is 21256515079. The reversal of 21256515078 is 87051565212.

It is a super-2 number, since 2×21256515078² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256515079) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 480775 + ... + 523122.

It is an arithmetic number, because the mean of its divisors is an integer number (2657819955).

Almost surely, 2^21256515078 is an apocalyptic number.

21256515078 is an abundant number, since it is smaller than the sum of its proper divisors (21268604202).

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

21256515078 is a wasteful number, since it uses less digits than its factorization.

21256515078 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1007431.

The product of its (nonzero) digits is 168000, while the sum is 42.

The spelling of 21256515078 in words is "twenty-one billion, two hundred fifty-six million, five hundred fifteen thousand, seventy-eight".