21607661 has 2 divisors, whose sum is σ = 21607662. Its totient is φ = 21607660.

The previous prime is 21607657. The next prime is 21607673. The reversal of 21607661 is 16670612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13801225 + 7806436 = 3715^2 + 2794^2 .

It is a cyclic number.

It is not a de Polignac number, because 21607661 - 2² = 21607657 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21607361) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10803830 + 10803831.

It is an arithmetic number, because the mean of its divisors is an integer number (10803831).

Almost surely, 2^21607661 is an apocalyptic number.

It is an amenable number.

21607661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21607661 is an equidigital number, since it uses as much as digits as its factorization.

21607661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3024, while the sum is 29.

The square root of 21607661 is about 4648.4041347542. The cubic root of 21607661 is about 278.5282513213.

The spelling of 21607661 in words is "twenty-one million, six hundred seven thousand, six hundred sixty-one".