21605961 has 16 divisors (see below), whose sum is σ = 31268160. Its totient is φ = 13191360.

The previous prime is 21605951. The next prime is 21605971. The reversal of 21605961 is 16950612.

It is an interprime number because it is at equal distance from previous prime (21605951) and next prime (21605971).

It is not a de Polignac number, because 21605961 - 2⁶ = 21605897 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21605911) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2995 + ... + 7223.

It is an arithmetic number, because the mean of its divisors is an integer number (1954260).

Almost surely, 2^21605961 is an apocalyptic number.

It is an amenable number.

21605961 is a deficient number, since it is larger than the sum of its proper divisors (9662199).

21605961 is a wasteful number, since it uses less digits than its factorization.

21605961 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4376.

The product of its (nonzero) digits is 3240, while the sum is 30.

The square root of 21605961 is about 4648.2212727021. The cubic root of 21605961 is about 278.5209466521.

The spelling of 21605961 in words is "twenty-one million, six hundred five thousand, nine hundred sixty-one".