21979561 has 4 divisors (see below), whose sum is σ = 23136400. Its totient is φ = 20822724.

The previous prime is 21979553. The next prime is 21979571. The reversal of 21979561 is 16597912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21979561 - 2³ = 21979553 is a prime.

It is a super-2 number, since 2×21979561² = 966202203505442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21979571) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 578391 + ... + 578428.

It is an arithmetic number, because the mean of its divisors is an integer number (5784100).

Almost surely, 2^21979561 is an apocalyptic number.

It is an amenable number.

21979561 is a deficient number, since it is larger than the sum of its proper divisors (1156839).

21979561 is a wasteful number, since it uses less digits than its factorization.

21979561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1156838.

The product of its digits is 34020, while the sum is 40.

The square root of 21979561 is about 4688.2364488153. The cubic root of 21979561 is about 280.1171321159.

The spelling of 21979561 in words is "twenty-one million, nine hundred seventy-nine thousand, five hundred sixty-one".