21361691 has 16 divisors (see below), whose sum is σ = 23940000. Its totient is φ = 18931968.

The previous prime is 21361619. The next prime is 21361709. The reversal of 21361691 is 19616312.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21361691 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21361091) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 42560 + ... + 43058.

It is an arithmetic number, because the mean of its divisors is an integer number (1496250).

Almost surely, 2^21361691 is an apocalyptic number.

21361691 is a deficient number, since it is larger than the sum of its proper divisors (2578309).

21361691 is a wasteful number, since it uses less digits than its factorization.

21361691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 638.

The product of its digits is 1944, while the sum is 29.

The square root of 21361691 is about 4621.8709415128. The cubic root of 21361691 is about 277.4673435044.

The spelling of 21361691 in words is "twenty-one million, three hundred sixty-one thousand, six hundred ninety-one".