21409661 has 16 divisors (see below), whose sum is σ = 26544000. Its totient is φ = 16815168.

The previous prime is 21409631. The next prime is 21409669. The reversal of 21409661 is 16690412.

It is a cyclic number.

It is not a de Polignac number, because 21409661 - 2¹⁸ = 21147517 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21409669) 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, 12770 + ... + 14348.

It is an arithmetic number, because the mean of its divisors is an integer number (1659000).

Almost surely, 2^21409661 is an apocalyptic number.

It is an amenable number.

21409661 is a deficient number, since it is larger than the sum of its proper divisors (5134339).

21409661 is a wasteful number, since it uses less digits than its factorization.

21409661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1748.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 21409661 is about 4627.0574882964. The cubic root of 21409661 is about 277.6748825952.

The spelling of 21409661 in words is "twenty-one million, four hundred nine thousand, six hundred sixty-one".