21405961 has 2 divisors, whose sum is σ = 21405962. Its totient is φ = 21405960.

The previous prime is 21405953. The next prime is 21405997. The reversal of 21405961 is 16950412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19855936 + 1550025 = 4456^2 + 1245^2 .

It is a cyclic number.

It is not a de Polignac number, because 21405961 - 2³ = 21405953 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21405931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10702980 + 10702981.

It is an arithmetic number, because the mean of its divisors is an integer number (10702981).

Almost surely, 2^21405961 is an apocalyptic number.

It is an amenable number.

21405961 is a deficient number, since it is larger than the sum of its proper divisors (1).

21405961 is an equidigital number, since it uses as much as digits as its factorization.

21405961 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21405961 is about 4626.6576488865. The cubic root of 21405961 is about 277.6588858254.

It can be divided in two parts, 21405 and 961, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21405961 in words is "twenty-one million, four hundred five thousand, nine hundred sixty-one".