21512225 has 36 divisors (see below), whose sum is σ = 32887404. Its totient is φ = 13870080.

The previous prime is 21512213. The next prime is 21512263. The reversal of 21512225 is 52221512.

It is a happy number.

It can be written as a sum of positive squares in 6 ways, for example, as 1940449 + 19571776 = 1393^2 + 4424^2 .

It is not a de Polignac number, because 21512225 - 2¹⁴ = 21495841 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21512197 and 21512206.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 20309 + ... + 21341.

It is an arithmetic number, because the mean of its divisors is an integer number (913539).

Almost surely, 2^21512225 is an apocalyptic number.

21512225 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21512225 is a deficient number, since it is larger than the sum of its proper divisors (11375179).

21512225 is a wasteful number, since it uses less digits than its factorization.

21512225 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1074 (or 1062 counting only the distinct ones).

The product of its digits is 400, while the sum is 20.

The square root of 21512225 is about 4638.1273160619. The cubic root of 21512225 is about 278.1175813364.

Adding to 21512225 its reverse (52221512), we get a palindrome (73733737).

The spelling of 21512225 in words is "twenty-one million, five hundred twelve thousand, two hundred twenty-five".