21011078731 has 4 divisors (see below), whose sum is σ = 22116925000. Its totient is φ = 19905232464.

The previous prime is 21011078729. The next prime is 21011078773. The reversal of 21011078731 is 13787011012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21011078731 - 2¹ = 21011078729 is a prime.

It is a super-2 number, since 2×21011078731² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21011078693 and 21011078702.

It is not an unprimeable number, because it can be changed into a prime (21011078701) 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, 552923106 + ... + 552923143.

It is an arithmetic number, because the mean of its divisors is an integer number (5529231250).

Almost surely, 2^21011078731 is an apocalyptic number.

21011078731 is a deficient number, since it is larger than the sum of its proper divisors (1105846269).

21011078731 is a wasteful number, since it uses less digits than its factorization.

21011078731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1105846268.

The product of its (nonzero) digits is 2352, while the sum is 31.

Adding to 21011078731 its reverse (13787011012), we get a palindrome (34798089743).

The spelling of 21011078731 in words is "twenty-one billion, eleven million, seventy-eight thousand, seven hundred thirty-one".