21506771 has 24 divisors (see below), whose sum is σ = 26562816. Its totient is φ = 17228640.

The previous prime is 21506753. The next prime is 21506843. The reversal of 21506771 is 17760512.

21506771 = 119² + 120² + ... + 404².

It is not a de Polignac number, because 21506771 - 2⁶ = 21506707 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 42506 + ... + 43008.

It is an arithmetic number, because the mean of its divisors is an integer number (1106784).

Almost surely, 2^21506771 is an apocalyptic number.

21506771 is a deficient number, since it is larger than the sum of its proper divisors (5056045).

21506771 is a wasteful number, since it uses less digits than its factorization.

21506771 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 563 (or 550 counting only the distinct ones).

The product of its (nonzero) digits is 2940, while the sum is 29.

The square root of 21506771 is about 4637.5393259788. The cubic root of 21506771 is about 278.0940756089.

It can be divided in two parts, 21 and 506771, that multiplied together give a triangular number (10642191 = T₄₆₁₃).

The spelling of 21506771 in words is "twenty-one million, five hundred six thousand, seven hundred seventy-one".