21420661 has 2 divisors, whose sum is σ = 21420662. Its totient is φ = 21420660.

The previous prime is 21420649. The next prime is 21420667. The reversal of 21420661 is 16602412.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17380561 + 4040100 = 4169^2 + 2010^2 .

It is a cyclic number.

It is not a de Polignac number, because 21420661 - 2¹⁵ = 21387893 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21420667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10710330 + 10710331.

It is an arithmetic number, because the mean of its divisors is an integer number (10710331).

Almost surely, 2^21420661 is an apocalyptic number.

It is an amenable number.

21420661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21420661 is an equidigital number, since it uses as much as digits as its factorization.

21420661 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 576, while the sum is 22.

The square root of 21420661 is about 4628.2459960551. The cubic root of 21420661 is about 277.7224296776.

The spelling of 21420661 in words is "twenty-one million, four hundred twenty thousand, six hundred sixty-one".