19956661 has 4 divisors (see below), whose sum is σ = 19992672. Its totient is φ = 19920652.

The previous prime is 19956659. The next prime is 19956679. The reversal of 19956661 is 16665991.

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 an emirpimes, since its reverse is a distinct semiprime: 16665991 = 109 ⋅152899.

It is a cyclic number.

It is not a de Polignac number, because 19956661 - 2¹ = 19956659 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19956641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17161 + ... + 18286.

It is an arithmetic number, because the mean of its divisors is an integer number (4998168).

Almost surely, 2^19956661 is an apocalyptic number.

It is an amenable number.

19956661 is a deficient number, since it is larger than the sum of its proper divisors (36011).

19956661 is an equidigital number, since it uses as much as digits as its factorization.

19956661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 36010.

The product of its digits is 87480, while the sum is 43.

The square root of 19956661 is about 4467.2878796872. The cubic root of 19956661 is about 271.2455529579.

The spelling of 19956661 in words is "nineteen million, nine hundred fifty-six thousand, six hundred sixty-one".