JSchlather
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 84 Can you answer my son's fourth-grade homework question: Which numbers are prime, have digits adding to ten and have a three in the tens place? 56 Paul Erdos's Two-Line Functional Analysis Proof 17 Compute $\operatorname{Hom}_{\mathbb{Z}} ( \mathbb{Q}, \mathbb{Z})$ 14 Non-associative, non-commutative binary operation with a identity 12 Why is the supremum of the empty set $-\infty$ and the infimum $\infty$?

### Reputation (11,544)

 +10 Show that for a finite metric space A, every subset is open +5 Whats the probability a subset of an $\mathbb F_2$ vector space is a spanning set? +20 Can we always find a primitive element that is a square? +10 Can you answer my son's fourth-grade homework question: Which numbers are prime, have digits adding to ten and have a three in the tens place?

### Questions (29)

 21 Bijection between $2^{\mathbb R}$ and $\mathbb{ R ^ R}$ 14 Why is the Long Line not a covering space for the Circle 12 Algebraic Proof that $\sum\limits_{i=0}^n \binom{n}{i}=2^n$ 12 Whats the probability a subset of an $\mathbb F_2$ vector space is a spanning set? 12 How is addition defined?

### Tags (105)

 255 abstract-algebra × 72 75 reference-request × 10 154 field-theory × 53 73 galois-theory × 25 118 general-topology × 40 70 real-analysis × 21 84 elementary-number-theory 70 group-theory × 18 84 recreational-mathematics 67 functional-analysis × 7

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 Mathematics 11,544 rep 32665 Stack Overflow 1,196 rep 819 TeX - LaTeX 386 rep 315 Area 51 151 rep 1 MathOverflow 123 rep 3