21978478457 has 16 divisors (see below), whose sum is σ = 23813903232. Its totient is φ = 20164045440.

The previous prime is 21978478451. The next prime is 21978478463. The reversal of 21978478457 is 75487487912.

It is an interprime number because it is at equal distance from previous prime (21978478451) and next prime (21978478463).

It is a cyclic number.

It is not a de Polignac number, because 21978478457 - 2⁶ = 21978478393 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21978478457.

It is not an unprimeable number, because it can be changed into a prime (21978478451) 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 15 ways as a sum of consecutive naturals, for example, 1814732 + ... + 1826802.

It is an arithmetic number, because the mean of its divisors is an integer number (1488368952).

Almost surely, 2^21978478457 is an apocalyptic number.

It is an amenable number.

21978478457 is a deficient number, since it is larger than the sum of its proper divisors (1835424775).

21978478457 is a wasteful number, since it uses less digits than its factorization.

21978478457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12928.

The product of its digits is 31610880, while the sum is 62.

The spelling of 21978478457 in words is "twenty-one billion, nine hundred seventy-eight million, four hundred seventy-eight thousand, four hundred fifty-seven".