21544661961 has 45 divisors (see below), whose sum is σ = 32978374429. Its totient is φ = 14016998376.

The previous prime is 21544661921. The next prime is 21544662019. The reversal of 21544661961 is 16916644512.

The square root of 21544661961 is 146781.

It is a perfect power (a square), and thus also a powerful number.

21544661961 is a `hidden beast` number, since 2 + 15 + 446 + 6 + 196 + 1 = 666.

It is not a de Polignac number, because 21544661961 - 2²⁵ = 21511107529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21544661911) by changing a digit.

It is a polite number, since it can be written in 44 ways as a sum of consecutive naturals, for example, 62088190 + ... + 62088536.

Almost surely, 2^21544661961 is an apocalyptic number.

21544661961 is the 146781-st square number.

21544661961 is the 73391-st centered octagonal number.

It is an amenable number.

21544661961 is a deficient number, since it is larger than the sum of its proper divisors (11433712468).

21544661961 is an frugal number, since it uses more digits than its factorization.

21544661961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 800 (or 397 counting only the distinct ones).

The product of its digits is 311040, while the sum is 45.

The spelling of 21544661961 in words is "twenty-one billion, five hundred forty-four million, six hundred sixty-one thousand, nine hundred sixty-one".