21512505 has 32 divisors (see below), whose sum is σ = 39564288. Its totient is φ = 9777600.

The previous prime is 21512501. The next prime is 21512507. The reversal of 21512505 is 50521512.

21512505 = 88² + 89² + ... + 402².

It is not a de Polignac number, because 21512505 - 2² = 21512501 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is not an unprimeable number, because it can be changed into a prime (21512501) 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, 21670 + ... + 22640.

It is an arithmetic number, because the mean of its divisors is an integer number (1236384).

Almost surely, 2^21512505 is an apocalyptic number.

It is an amenable number.

21512505 is a deficient number, since it is larger than the sum of its proper divisors (18051783).

21512505 is a wasteful number, since it uses less digits than its factorization.

21512505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1197.

The product of its (nonzero) digits is 500, while the sum is 21.

The square root of 21512505 is about 4638.1575005599. The cubic root of 21512505 is about 278.1187879772.

It can be divided in two parts, 2151 and 2505, that added together give a triangular number (4656 = T₉₆).

The spelling of 21512505 in words is "twenty-one million, five hundred twelve thousand, five hundred five".