21318961 has 2 divisors, whose sum is σ = 21318962. Its totient is φ = 21318960.

The previous prime is 21318959. The next prime is 21318967. The reversal of 21318961 is 16981312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21298225 + 20736 = 4615^2 + 144^2 .

It is a cyclic number.

It is not a de Polignac number, because 21318961 - 2¹ = 21318959 is a prime.

Together with 21318959, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21318967) 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 as a sum of consecutive naturals, namely, 10659480 + 10659481.

It is an arithmetic number, because the mean of its divisors is an integer number (10659481).

Almost surely, 2^21318961 is an apocalyptic number.

It is an amenable number.

21318961 is a deficient number, since it is larger than the sum of its proper divisors (1).

21318961 is an equidigital number, since it uses as much as digits as its factorization.

21318961 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2592, while the sum is 31.

The square root of 21318961 is about 4617.2460406610. The cubic root of 21318961 is about 277.2822131274.

The spelling of 21318961 in words is "twenty-one million, three hundred eighteen thousand, nine hundred sixty-one".