Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
42	Adding Reversed Numbers	99	59343	6 4
25942	Ball sum	41	1648	11 11
30826	Bernoulli numbers	4	6	23 12
24998	PLAYING WITH BITS	33	709	13 13
36670	Bipartite Permutation	11	309	5 14
17921	XOR	-16	6057	1 1
18294	Problem1	1	67	1 6
26314	Corn Headache	7	326	8 9
34620	Crying Series	1	70	1 5
40400	Count Set Bits	-2	73	1 1
27269	Cube Numbers	29	586	9 11
22403	Divisors of factorial	67	1668	14 14
27299	Find Log	1	107	1 1
25311	Candies	8	986	6 7
32445	COUNT JUMPS	1	81	4 1
40512	Kevin likes array		3
25583	Easy Odd Sum	6	1399	4 4
35294	Tricky Means		187	17 1
31	Fast Multiplication	48	6099	14 12
16272	Nanoworld	1	35	17 17
25008	New Currency Shopping	1	9	34 17
36963	Nobabs Treasure Hunt	-1	46	1 1
35296	Prime or not Prime!	1	447	1 1
15708	Divisibility	13	6438	4 3
17104	Fun with Sequences (Act 3)	2	1700	1 1
17126	Fun with Sequences (Act 4)	2	857	1 1
17481	Fun with Sequences (Act 5)		642	1 1
18011	Fun with Sequences (Act 6)		824	1 1
18012	Fun with Sequences (Act 7)		722	1 1
176	Sum of one-sequence	5	641	11 27
22455	SUM OF PRODUCT	33	961	18 21
35293	Sums to calculate	2	328	1 1
35297	Trial Division	1	75	17 1
235	Very Fast Multiplication	22	1045	26 22

The problem involves but simple mathematical concepts like arithmetic operations

http://www.basic-mathematics.com