21221535541661 has 16 divisors (see below), whose sum is σ = 26561504726400. Its totient is φ = 16506077928768.

The previous prime is 21221535541651. The next prime is 21221535541663. The reversal of 21221535541661 is 16614553512212.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21221535541661 - 2⁶ = 21221535541597 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221535541663) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1976297066 + ... + 1976307803.

It is an arithmetic number, because the mean of its divisors is an integer number (1660094045400).

Almost surely, 2^{21221535541661} is an apocalyptic number.

It is an amenable number.

21221535541661 is a deficient number, since it is larger than the sum of its proper divisors (5339969184739).

21221535541661 is a wasteful number, since it uses less digits than its factorization.

21221535541661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3952604948.

The product of its digits is 432000, while the sum is 44.

The spelling of 21221535541661 in words is "twenty-one trillion, two hundred twenty-one billion, five hundred thirty-five million, five hundred forty-one thousand, six hundred sixty-one".