21661016 has 16 divisors (see below), whose sum is σ = 43738800. Its totient is φ = 9997344.

The previous prime is 21661001. The next prime is 21661027. The reversal of 21661016 is 61016612.

21661016 = T₁₈₁₉ + T₁₈₂₀ + ... + T₁₈₃₁.

It is a super-2 number, since 2×21661016² = 938399228304512, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21660982 and 21661000.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 104036 + ... + 104243.

It is an arithmetic number, because the mean of its divisors is an integer number (2733675).

Almost surely, 2^21661016 is an apocalyptic number.

21661016 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

21661016 is an abundant number, since it is smaller than the sum of its proper divisors (22077784).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21661016 is a wasteful number, since it uses less digits than its factorization.

21661016 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 208298 (or 208294 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 21661016 is about 4654.1396627089. The cubic root of 21661016 is about 278.7573160621.

Adding to 21661016 its reverse (61016612), we get a palindrome (82677628).

The spelling of 21661016 in words is "twenty-one million, six hundred sixty-one thousand, sixteen".