21278669 has 2 divisors, whose sum is σ = 21278670. Its totient is φ = 21278668.

The previous prime is 21278659. The next prime is 21278671. The reversal of 21278669 is 96687212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21252100 + 26569 = 4610^2 + 163^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21278669 is a prime.

It is a super-2 number, since 2×21278669² = 905563508823122, which contains 22 as substring.

Together with 21278671, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21278659) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10639334 + 10639335.

It is an arithmetic number, because the mean of its divisors is an integer number (10639335).

Almost surely, 2^21278669 is an apocalyptic number.

It is an amenable number.

21278669 is a deficient number, since it is larger than the sum of its proper divisors (1).

21278669 is an equidigital number, since it uses as much as digits as its factorization.

21278669 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72576, while the sum is 41.

The square root of 21278669 is about 4612.8807701912. The cubic root of 21278669 is about 277.1074187944.

The spelling of 21278669 in words is "twenty-one million, two hundred seventy-eight thousand, six hundred sixty-nine".