21375661 has 2 divisors, whose sum is σ = 21375662. Its totient is φ = 21375660.

The previous prime is 21375659. The next prime is 21375721. The reversal of 21375661 is 16657312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19980900 + 1394761 = 4470^2 + 1181^2 .

It is a cyclic number.

It is not a de Polignac number, because 21375661 - 2¹ = 21375659 is a prime.

Together with 21375659, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21375611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10687830 + 10687831.

It is an arithmetic number, because the mean of its divisors is an integer number (10687831).

Almost surely, 2^21375661 is an apocalyptic number.

It is an amenable number.

21375661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21375661 is an equidigital number, since it uses as much as digits as its factorization.

21375661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 7560, while the sum is 31.

The square root of 21375661 is about 4623.3819872470. The cubic root of 21375661 is about 277.5278158412.

The spelling of 21375661 in words is "twenty-one million, three hundred seventy-five thousand, six hundred sixty-one".