21203453661 has 32 divisors (see below), whose sum is σ = 31069261440. Its totient is φ = 12782880000.

The previous prime is 21203453659. The next prime is 21203453669. The reversal of 21203453661 is 16635430212.

It is not a de Polignac number, because 21203453661 - 2¹ = 21203453659 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21203453669) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 579375 + ... + 614883.

It is an arithmetic number, because the mean of its divisors is an integer number (970914420).

Almost surely, 2^21203453661 is an apocalyptic number.

It is an amenable number.

21203453661 is a deficient number, since it is larger than the sum of its proper divisors (9865807779).

21203453661 is a wasteful number, since it uses less digits than its factorization.

21203453661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35837.

The product of its (nonzero) digits is 25920, while the sum is 33.

Adding to 21203453661 its reverse (16635430212), we get a palindrome (37838883873).

The spelling of 21203453661 in words is "twenty-one billion, two hundred three million, four hundred fifty-three thousand, six hundred sixty-one".