72121561 has 4 divisors (see below), whose sum is σ = 72581092. Its totient is φ = 71662032.

The previous prime is 72121559. The next prime is 72121573. The reversal of 72121561 is 16512127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16512127 = 4001 ⋅4127.

It can be written as a sum of positive squares in 2 ways, for example, as 17065161 + 55056400 = 4131^2 + 7420^2 .

It is a cyclic number.

It is not a de Polignac number, because 72121561 - 2¹ = 72121559 is a prime.

It is a super-2 number, since 2×72121561² = 10403039122153442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (72121961) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 229530 + ... + 229843.

It is an arithmetic number, because the mean of its divisors is an integer number (18145273).

Almost surely, 2^72121561 is an apocalyptic number.

It is an amenable number.

72121561 is a deficient number, since it is larger than the sum of its proper divisors (459531).

72121561 is a wasteful number, since it uses less digits than its factorization.

72121561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 459530.

The product of its digits is 840, while the sum is 25.

The square root of 72121561 is about 8492.4414039780. The cubic root of 72121561 is about 416.2507598876.

Adding to 72121561 its reverse (16512127), we get a palindrome (88633688).

The spelling of 72121561 in words is "seventy-two million, one hundred twenty-one thousand, five hundred sixty-one".