21661411447661 has 4 divisors (see below), whose sum is σ = 22801485734400. Its totient is φ = 20521337160924.

The previous prime is 21661411447651. The next prime is 21661411447733. The reversal of 21661411447661 is 16674411416612.

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 a de Polignac number, because none of the positive numbers 2^k-21661411447661 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 (21661411447651) 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, 570037143341 + ... + 570037143378.

It is an arithmetic number, because the mean of its divisors is an integer number (5700371433600).

Almost surely, 2^{21661411447661} is an apocalyptic number.

It is an amenable number.

21661411447661 is a deficient number, since it is larger than the sum of its proper divisors (1140074286739).

21661411447661 is a wasteful number, since it uses less digits than its factorization.

21661411447661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1140074286738.

The product of its digits is 1161216, while the sum is 50.

The spelling of 21661411447661 in words is "twenty-one trillion, six hundred sixty-one billion, four hundred eleven million, four hundred forty-seven thousand, six hundred sixty-one".