21505929201 has 9 divisors (see below), whose sum is σ = 31064755449. Its totient is φ = 14336992836.

The previous prime is 21505929161. The next prime is 21505929259. The reversal of 21505929201 is 10292950512.

It is a happy number.

The square root of 21505929201 is 146649.

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

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 21505929201 - 2¹⁷ = 21505798129 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21505929001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 415506 + ... + 464388.

Almost surely, 2^21505929201 is an apocalyptic number.

21505929201 is the 146649-th square number.

21505929201 is the 73325-th centered octagonal number.

It is an amenable number.

21505929201 is a deficient number, since it is larger than the sum of its proper divisors (9558826248).

21505929201 is an frugal number, since it uses more digits than its factorization.

21505929201 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 97772 (or 48886 counting only the distinct ones).

The product of its (nonzero) digits is 16200, while the sum is 36.

Multiplying 21505929201 by its sum of digits (36), we get a square (774213451236 = 879894²).

The spelling of 21505929201 in words is "twenty-one billion, five hundred five million, nine hundred twenty-nine thousand, two hundred one".