Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
42	Adding Reversed Numbers	100	65453	6 4
25942	Ball sum	41	1709	11 11
30826	Bernoulli numbers	4	6	23 12
24998	PLAYING WITH BITS	33	744	13 13
36670	Bipartite Permutation	11	329	5 14
17921	XOR	-15	6771	1 1
18294	Problem1	1	68	1 6
26314	Corn Headache	7	335	8 9
34620	Crying Series	1	76	1 5
40400	Count Set Bits	-2	162	1 1
27269	Cube Numbers	29	597	9 11
22403	Divisors of factorial	69	1755	14 14
27299	Find Log	1	113	1 1
25311	Candies	9	1026	6 7
32445	COUNT JUMPS	1	86	4 1
40512	Kevin likes array		13
25583	Easy Odd Sum	6	1539	4 4
35294	Tricky Means		207	17 1
31	Fast Multiplication	48	7190	14 12
16272	Nanoworld	1	35	17 17
25008	New Currency Shopping	1	9	34 17
36963	Nobabs Treasure Hunt	-1	52	1 1
35296	Prime or not Prime!	1	599	1 1
15708	Divisibility	13	7043	4 3
17104	Fun with Sequences (Act 3)	3	1856	1 1
17126	Fun with Sequences (Act 4)	2	934	1 1
17481	Fun with Sequences (Act 5)	1	671	1 1
18011	Fun with Sequences (Act 6)	1	931	1 1
18012	Fun with Sequences (Act 7)		810	1 1
176	Sum of one-sequence	5	650	11 27
22455	SUM OF PRODUCT	34	997	18 20
35293	Sums to calculate	2	382	1 1
35297	Trial Division	1	98	17 1
235	Very Fast Multiplication	22	1156	26 22

The problem involves but simple mathematical concepts like arithmetic operations

http://www.basic-mathematics.com