Properties of the Number 721

Seven Hundred Twenty-One

Basics

Value: 720 → 721 → 722

Parity: odd

Prime: No

Previous Prime: 719

Next Prime: 727

Digit Sum: 10

Digital Root: 1

Palindrome: No

Factorization: 7 × 103

Divisors: 1, 7, 103, 721

Polygonal

Triangular: No

Square: No

Pentagonal: No

Hexagonal: No

Heptagonal: No

Tetrahedral: No

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Representations

Binary: 1011010001

Octal: 1321

Duodecimal: 501

Hexadecimal: 2d1

Square: 519841

Square Root: 26.851443164195103

Classification

Fibonacci: No

Bell Number: No

Factorial Number: No

Regular Number: No

Perfect Number: No

Special

Kaprekar Constant: No

Munchausen Constant: No

Armstrong Number: No

Kaprekar Number: No

Catalan Number: No

Vampire Number: No

Taxicab Number: No

Super Prime: No

Friedman Number: No

Fermat Number: No

Cullen Number: No

OEIS Sequences

Hex (or centered hexagonal) numbers: 3·n*(n+1)+1 (crystal ball sequence for hexagonal lattice). A3215

a(n) = n! + 1. A38507

a(n) = 2·n² - 1. A56220

Number of steps until the RADD sequence T(k+1) = n + R(T(k)), T(0) = 1, enters a cycle; -1 if no cycle is ever reached. (R=A004086: reverse digits). A117816

Generalized 9-gonal (or enneagonal) numbers: m*(7·m - 5)/2 with m = 0, 1, -1, 2, -2, 3, -3, ... A118277

Numbers obtained by reinterpreting base-2 representation of n in the factorial base: a(n) = ∑_k>=0 A030308(n,k)*A000142(k+1). A59590

a(n) = least positive k such that the remainder when 3^k is divided by k is n. A78457

Sum of factorials of the digits of n. A61602

Number of partitions of n into distinct parts for which (number of odd parts) = (number of even parts). A239241

Triangle read by rows: T(n,k) is the number of inequivalent colorings of lone-child-avoiding rooted trees with n colored leaves using exactly k colors. A339645