21507689025 has 45 divisors (see below), whose sum is σ = 39851903091. Its totient is φ = 11467247760.

The previous prime is 21507689023. The next prime is 21507689029. The reversal of 21507689025 is 52098670512.

The square root of 21507689025 is 146655.

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

It can be written as a sum of positive squares in only one way, i.e., 7742768049 + 13764920976 = 87993^2 + 117324^2 .

It is a tau number, because it is divible by the number of its divisors (45).

It is not a de Polignac number, because 21507689025 - 2¹ = 21507689023 is a prime.

It is a super-2 number, since 2×21507689025² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21507689023) 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, 6597846 + ... + 6601104.

Almost surely, 2^21507689025 is an apocalyptic number.

21507689025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21507689025 is the 146655-th square number.

21507689025 is the 73328-th centered octagonal number.

It is an amenable number.

21507689025 is a deficient number, since it is larger than the sum of its proper divisors (18344214066).

21507689025 is an frugal number, since it uses more digits than its factorization.

21507689025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6540 (or 3267 counting only the distinct ones).

The product of its (nonzero) digits is 302400, while the sum is 45.

The spelling of 21507689025 in words is "twenty-one billion, five hundred seven million, six hundred eighty-nine thousand, twenty-five".