21679661 has 2 divisors, whose sum is σ = 21679662. Its totient is φ = 21679660.

The previous prime is 21679631. The next prime is 21679663. The reversal of 21679661 is 16697612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16362025 + 5317636 = 4045^2 + 2306^2 .

It is a cyclic number.

It is not a de Polignac number, because 21679661 - 2¹⁴ = 21663277 is a prime.

Together with 21679663, 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 (21679663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10839830 + 10839831.

It is an arithmetic number, because the mean of its divisors is an integer number (10839831).

Almost surely, 2^21679661 is an apocalyptic number.

It is an amenable number.

21679661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21679661 is an equidigital number, since it uses as much as digits as its factorization.

21679661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 27216, while the sum is 38.

The square root of 21679661 is about 4656.1422873447. The cubic root of 21679661 is about 278.8372744478.

The spelling of 21679661 in words is "twenty-one million, six hundred seventy-nine thousand, six hundred sixty-one".