21278348591 has 4 divisors (see below), whose sum is σ = 21278645472. Its totient is φ = 21278051712.

The previous prime is 21278348573. The next prime is 21278348659. The reversal of 21278348591 is 19584387212.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21278348591 - 2²⁶ = 21211239727 is a prime.

It is a super-2 number, since 2×21278348591² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21278348561) 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 3 ways as a sum of consecutive naturals, for example, 32975 + ... + 208911.

It is an arithmetic number, because the mean of its divisors is an integer number (5319661368).

Almost surely, 2^21278348591 is an apocalyptic number.

21278348591 is a deficient number, since it is larger than the sum of its proper divisors (296881).

21278348591 is a wasteful number, since it uses less digits than its factorization.

21278348591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 296880.

The product of its digits is 967680, while the sum is 50.

Adding to 21278348591 its sum of digits (50), we get a square (21278348641 = 145871²).

The spelling of 21278348591 in words is "twenty-one billion, two hundred seventy-eight million, three hundred forty-eight thousand, five hundred ninety-one".