21978311 has 2 divisors, whose sum is σ = 21978312. Its totient is φ = 21978310.

The previous prime is 21978301. The next prime is 21978343. The reversal of 21978311 is 11387912.

It is an a-pointer prime, because the next prime (21978343) can be obtained adding 21978311 to its sum of digits (32).

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21978311 - 2⁶ = 21978247 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21978301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10989155 + 10989156.

It is an arithmetic number, because the mean of its divisors is an integer number (10989156).

Almost surely, 2^21978311 is an apocalyptic number.

21978311 is a deficient number, since it is larger than the sum of its proper divisors (1).

21978311 is an equidigital number, since it uses as much as digits as its factorization.

21978311 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3024, while the sum is 32.

The square root of 21978311 is about 4688.1031345311. The cubic root of 21978311 is about 280.1118218331. Note that the first 3 decimals are identical.

The spelling of 21978311 in words is "twenty-one million, nine hundred seventy-eight thousand, three hundred eleven".