21961993 has 2 divisors, whose sum is σ = 21961994. Its totient is φ = 21961992.

The previous prime is 21961991. The next prime is 21962021. The reversal of 21961993 is 39916912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17909824 + 4052169 = 4232^2 + 2013^2 .

It is a cyclic number.

It is not a de Polignac number, because 21961993 - 2¹ = 21961991 is a prime.

Together with 21961991, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21961991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10980996 + 10980997.

It is an arithmetic number, because the mean of its divisors is an integer number (10980997).

Almost surely, 2^21961993 is an apocalyptic number.

It is an amenable number.

21961993 is a deficient number, since it is larger than the sum of its proper divisors (1).

21961993 is an equidigital number, since it uses as much as digits as its factorization.

21961993 is an evil number, because the sum of its binary digits is even.

The product of its digits is 26244, while the sum is 40.

The square root of 21961993 is about 4686.3624486375. The cubic root of 21961993 is about 280.0424807995.

The spelling of 21961993 in words is "twenty-one million, nine hundred sixty-one thousand, nine hundred ninety-three".