21661705 has 16 divisors (see below), whose sum is σ = 28191744. Its totient is φ = 15883200.

The previous prime is 21661693. The next prime is 21661709. The reversal of 21661705 is 50716612.

It is not a de Polignac number, because 21661705 - 2¹¹ = 21659657 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21661709) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8712 + ... + 10918.

It is an arithmetic number, because the mean of its divisors is an integer number (1761984).

Almost surely, 2^21661705 is an apocalyptic number.

It is an amenable number.

21661705 is a deficient number, since it is larger than the sum of its proper divisors (6530039).

21661705 is a wasteful number, since it uses less digits than its factorization.

21661705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2376.

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

The square root of 21661705 is about 4654.2136822454. The cubic root of 21661705 is about 278.7602716291.

It can be divided in two parts, 21661 and 705, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21661705 in words is "twenty-one million, six hundred sixty-one thousand, seven hundred five".