21666872551 has 16 divisors (see below), whose sum is σ = 23154405120. Its totient is φ = 20225620800.

The previous prime is 21666872543. The next prime is 21666872561. The reversal of 21666872551 is 15527866612.

It is a cyclic number.

It is not a de Polignac number, because 21666872551 - 2³ = 21666872543 is a prime.

It is a super-2 number, since 2×21666872551² (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 = 21666872495 and 21666872504.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666872561) 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, 1236451 + ... + 1253851.

It is an arithmetic number, because the mean of its divisors is an integer number (1447150320).

Almost surely, 2^21666872551 is an apocalyptic number.

21666872551 is a deficient number, since it is larger than the sum of its proper divisors (1487532569).

21666872551 is a wasteful number, since it uses less digits than its factorization.

21666872551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18726.

The product of its digits is 1209600, while the sum is 49.

The spelling of 21666872551 in words is "twenty-one billion, six hundred sixty-six million, eight hundred seventy-two thousand, five hundred fifty-one".