21566961 has 12 divisors (see below), whose sum is σ = 33548788. Its totient is φ = 13271904.

The previous prime is 21566953. The next prime is 21566971. The reversal of 21566961 is 16966512.

21566961 is a `hidden beast` number, since 2 + 1 + 566 + 96 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 3240000 + 18326961 = 1800^2 + 4281^2 .

It is not a de Polignac number, because 21566961 - 2³ = 21566953 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21566911) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 92050 + ... + 92283.

Almost surely, 2^21566961 is an apocalyptic number.

It is an amenable number.

21566961 is a deficient number, since it is larger than the sum of its proper divisors (11981827).

21566961 is a wasteful number, since it uses less digits than its factorization.

21566961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 184352 (or 184349 counting only the distinct ones).

The product of its digits is 19440, while the sum is 36.

The square root of 21566961 is about 4644.0242247430. The cubic root of 21566961 is about 278.3532636196.

It can be divided in two parts, 215 and 66961, that added together give a palindrome (67176).

The spelling of 21566961 in words is "twenty-one million, five hundred sixty-six thousand, nine hundred sixty-one".