21377521 has 4 divisors (see below), whose sum is σ = 23320944. Its totient is φ = 19434100.

The previous prime is 21377519. The next prime is 21377549. The reversal of 21377521 is 12577312.

21377521 = T₁₉₆₆ + T₁₉₆₇ + ... + T₁₉₇₆.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21377521 - 2¹ = 21377519 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21377521.

It is not an unprimeable number, because it can be changed into a prime (21377501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 971695 + ... + 971716.

It is an arithmetic number, because the mean of its divisors is an integer number (5830236).

Almost surely, 2^21377521 is an apocalyptic number.

It is an amenable number.

21377521 is a deficient number, since it is larger than the sum of its proper divisors (1943423).

21377521 is a wasteful number, since it uses less digits than its factorization.

21377521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1943422.

The product of its digits is 2940, while the sum is 28.

The square root of 21377521 is about 4623.5831343234. The cubic root of 21377521 is about 277.5358652884.

The spelling of 21377521 in words is "twenty-one million, three hundred seventy-seven thousand, five hundred twenty-one".