21879661 has 2 divisors, whose sum is σ = 21879662. Its totient is φ = 21879660.

The previous prime is 21879643. The next prime is 21879701. The reversal of 21879661 is 16697812.

It is an a-pointer prime, because the next prime (21879701) can be obtained adding 21879661 to its sum of digits (40).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12460900 + 9418761 = 3530^2 + 3069^2 .

It is a cyclic number.

It is not a de Polignac number, because 21879661 - 2¹⁵ = 21846893 is a prime.

It is a plaindrome in base 8.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21879631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10939830 + 10939831.

It is an arithmetic number, because the mean of its divisors is an integer number (10939831).

Almost surely, 2^21879661 is an apocalyptic number.

It is an amenable number.

21879661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21879661 is an equidigital number, since it uses as much as digits as its factorization.

21879661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 40.

The square root of 21879661 is about 4677.5699887869. The cubic root of 21879661 is about 279.6920977636.

The spelling of 21879661 in words is "twenty-one million, eight hundred seventy-nine thousand, six hundred sixty-one".