21691279 has 2 divisors, whose sum is σ = 21691280. Its totient is φ = 21691278.

The previous prime is 21691273. The next prime is 21691283. The reversal of 21691279 is 97219612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21691279 - 2⁵ = 21691247 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21691273) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845639 + 10845640.

It is an arithmetic number, because the mean of its divisors is an integer number (10845640).

Almost surely, 2^21691279 is an apocalyptic number.

21691279 is a deficient number, since it is larger than the sum of its proper divisors (1).

21691279 is an equidigital number, since it uses as much as digits as its factorization.

21691279 is an evil number, because the sum of its binary digits is even.

The product of its digits is 13608, while the sum is 37.

The square root of 21691279 is about 4657.3897195747. The cubic root of 21691279 is about 278.8870746260.

The spelling of 21691279 in words is "twenty-one million, six hundred ninety-one thousand, two hundred seventy-nine".