20956561 has 4 divisors (see below), whose sum is σ = 20966400. Its totient is φ = 20946724.

The previous prime is 20956511. The next prime is 20956583. The reversal of 20956561 is 16565902.

It is a happy number.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 20956561 - 2¹⁹ = 20432273 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20956511) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 241 + ... + 6478.

It is an arithmetic number, because the mean of its divisors is an integer number (5241600).

Almost surely, 2^20956561 is an apocalyptic number.

It is an amenable number.

20956561 is a deficient number, since it is larger than the sum of its proper divisors (9839).

20956561 is an equidigital number, since it uses as much as digits as its factorization.

20956561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9838.

The product of its (nonzero) digits is 16200, while the sum is 34.

The square root of 20956561 is about 4577.8336579653. The cubic root of 20956561 is about 275.7020563105.

The spelling of 20956561 in words is "twenty million, nine hundred fifty-six thousand, five hundred sixty-one".