21417561 has 32 divisors (see below), whose sum is σ = 35568000. Its totient is φ = 12623040.

The previous prime is 21417553. The next prime is 21417587. The reversal of 21417561 is 16571412.

It is a happy number.

It is not a de Polignac number, because 21417561 - 2³ = 21417553 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21412561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 10015 + ... + 11963.

It is an arithmetic number, because the mean of its divisors is an integer number (1111500).

Almost surely, 2^21417561 is an apocalyptic number.

It is an amenable number.

21417561 is a deficient number, since it is larger than the sum of its proper divisors (14150439).

21417561 is a wasteful number, since it uses less digits than its factorization.

21417561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2006 (or 2000 counting only the distinct ones).

The product of its digits is 1680, while the sum is 27.

The square root of 21417561 is about 4627.9110838477. The cubic root of 21417561 is about 277.7090316929.

Adding to 21417561 its reverse (16571412), we get a palindrome (37988973).

The spelling of 21417561 in words is "twenty-one million, four hundred seventeen thousand, five hundred sixty-one".