21765601 has 24 divisors (see below), whose sum is σ = 26209512. Its totient is φ = 17952000.

The previous prime is 21765599. The next prime is 21765637. The reversal of 21765601 is 10656712.

It can be written as a sum of positive squares in 4 ways, for example, as 5645376 + 16120225 = 2376^2 + 4015^2 .

It is not a de Polignac number, because 21765601 - 2¹ = 21765599 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 21765601.

It is not an unprimeable number, because it can be changed into a prime (21765101) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 158805 + ... + 158941.

It is an arithmetic number, because the mean of its divisors is an integer number (1092063).

Almost surely, 2^21765601 is an apocalyptic number.

It is an amenable number.

21765601 is a deficient number, since it is larger than the sum of its proper divisors (4443911).

21765601 is a wasteful number, since it uses less digits than its factorization.

21765601 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 273 (or 262 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21765601 is about 4665.3618294833. The cubic root of 21765601 is about 279.2052334728.

Subtracting from 21765601 its reverse (10656712), we obtain a square (11108889 = 3333²).

It can be divided in two parts, 21765 and 601, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21765601 in words is "twenty-one million, seven hundred sixty-five thousand, six hundred one".