21651697 has 12 divisors (see below), whose sum is σ = 23483316. Its totient is φ = 19945440.

The previous prime is 21651691. The next prime is 21651701. The reversal of 21651697 is 79615612.

It can be written as a sum of positive squares in 2 ways, for example, as 18113536 + 3538161 = 4256^2 + 1881^2 .

It is not a de Polignac number, because 21651697 - 2³ = 21651689 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651691) 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 11 ways as a sum of consecutive naturals, for example, 12547 + ... + 14167.

It is an arithmetic number, because the mean of its divisors is an integer number (1956943).

Almost surely, 2^21651697 is an apocalyptic number.

It is an amenable number.

21651697 is a deficient number, since it is larger than the sum of its proper divisors (1831619).

21651697 is a wasteful number, since it uses less digits than its factorization.

21651697 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1696 (or 1677 counting only the distinct ones).

The product of its digits is 22680, while the sum is 37.

The square root of 21651697 is about 4653.1384032715. The cubic root of 21651697 is about 278.7173346803.

The spelling of 21651697 in words is "twenty-one million, six hundred fifty-one thousand, six hundred ninety-seven".