21667657961 has 4 divisors (see below), whose sum is σ = 21668007492. Its totient is φ = 21667308432.

The previous prime is 21667657937. The next prime is 21667657981. The reversal of 21667657961 is 16975676612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 6527832025 + 15139825936 = 80795^2 + 123044^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21667657961 is a prime.

It is a super-3 number, since 3×21667657961³ (a number of 32 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21667657897 and 21667657906.

It is not an unprimeable number, because it can be changed into a prime (21667657981) 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, 53930 + ... + 215043.

It is an arithmetic number, because the mean of its divisors is an integer number (5417001873).

Almost surely, 2^21667657961 is an apocalyptic number.

It is an amenable number.

21667657961 is a deficient number, since it is larger than the sum of its proper divisors (349531).

21667657961 is an equidigital number, since it uses as much as digits as its factorization.

21667657961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 349530.

The product of its digits is 5715360, while the sum is 56.

The spelling of 21667657961 in words is "twenty-one billion, six hundred sixty-seven million, six hundred fifty-seven thousand, nine hundred sixty-one".