21506117051 has 4 divisors (see below), whose sum is σ = 22006259352. Its totient is φ = 21005974752.

The previous prime is 21506117033. The next prime is 21506117057. The reversal of 21506117051 is 15071160512.

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 21506117051 - 2¹⁴ = 21506100667 is a prime.

It is a super-2 number, since 2×21506117051² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21506117057) 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, 250071086 + ... + 250071171.

It is an arithmetic number, because the mean of its divisors is an integer number (5501564838).

Almost surely, 2^21506117051 is an apocalyptic number.

21506117051 is a deficient number, since it is larger than the sum of its proper divisors (500142301).

21506117051 is an equidigital number, since it uses as much as digits as its factorization.

21506117051 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 500142300.

The product of its (nonzero) digits is 2100, while the sum is 29.

Adding to 21506117051 its reverse (15071160512), we get a palindrome (36577277563).

The spelling of 21506117051 in words is "twenty-one billion, five hundred six million, one hundred seventeen thousand, fifty-one".