21939997 has 2 divisors, whose sum is σ = 21939998. Its totient is φ = 21939996.

The previous prime is 21939977. The next prime is 21940027. The reversal of 21939997 is 79993912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12243001 + 9696996 = 3499^2 + 3114^2 .

It is a cyclic number.

It is not a de Polignac number, because 21939997 - 2¹⁵ = 21907229 is a prime.

It is a super-3 number, since 3×21939997³ (a number of 23 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21939997.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21939937) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10969998 + 10969999.

It is an arithmetic number, because the mean of its divisors is an integer number (10969999).

Almost surely, 2^21939997 is an apocalyptic number.

It is an amenable number.

21939997 is a deficient number, since it is larger than the sum of its proper divisors (1).

21939997 is an equidigital number, since it uses as much as digits as its factorization.

21939997 is an evil number, because the sum of its binary digits is even.

The product of its digits is 275562, while the sum is 49.

The square root of 21939997 is about 4684.0150512141. The cubic root of 21939997 is about 279.9489575325.

The spelling of 21939997 in words is "twenty-one million, nine hundred thirty-nine thousand, nine hundred ninety-seven".