20556661 has 4 divisors (see below), whose sum is σ = 20569824. Its totient is φ = 20543500.

The previous prime is 20556647. The next prime is 20556667. The reversal of 20556661 is 16665502.

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 20556661 - 2⁷ = 20556533 is a prime.

It is a super-2 number, since 2×20556661² = 845152622937842, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20556667) 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, 3865 + ... + 7486.

It is an arithmetic number, because the mean of its divisors is an integer number (5142456).

Almost surely, 2^20556661 is an apocalyptic number.

It is an amenable number.

20556661 is a deficient number, since it is larger than the sum of its proper divisors (13163).

20556661 is a wasteful number, since it uses less digits than its factorization.

20556661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13162.

The product of its (nonzero) digits is 10800, while the sum is 31.

The square root of 20556661 is about 4533.9454121107. The cubic root of 20556661 is about 273.9371026176.

The spelling of 20556661 in words is "twenty million, five hundred fifty-six thousand, six hundred sixty-one".