Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
42	Adding Reversed Numbers	96	57214	6 4
25942	Ball sum	40	1627	11 11
30826	Bernoulli numbers	4	6	23 12
24998	PLAYING WITH BITS	33	687	13 13
36670	Bipartite Permutation	10	294	6 16
17921	XOR	-16	5863	1 1
18294	Problem1	1	67	1 6
26314	Corn Headache	7	326	8 9
34620	Crying Series	1	69	1 5
40400	Count Set Bits	-1	52	1 1
27269	Cube Numbers	29	585	9 11
22403	Divisors of factorial	64	1618	14 14
27299	Find Log	1	107	1 1
25311	Candies	8	966	6 7
32445	COUNT JUMPS	1	80	4 1
40512	Kevin likes array		3
25583	Easy Odd Sum	5	1369	4 4
35294	Tricky Means		179	17 1
31	Fast Multiplication	47	5827	15 12
16272	Nanoworld	1	35	17 17
25008	New Currency Shopping	1	9	34 17
36963	Nobabs Treasure Hunt	-1	43	1 1
35296	Prime or not Prime!	1	400	1 1
15708	Divisibility	13	6270	4 3
17104	Fun with Sequences (Act 3)	2	1674	1 1
17126	Fun with Sequences (Act 4)	2	849	1 1
17481	Fun with Sequences (Act 5)		635	1 1
18011	Fun with Sequences (Act 6)		817	1 1
18012	Fun with Sequences (Act 7)		717	1 1
176	Sum of one-sequence	5	640	11 27
22455	SUM OF PRODUCT	33	953	18 21
35293	Sums to calculate	2	311	1 1
35297	Trial Division	1	65	17 1
235	Very Fast Multiplication	22	1005	26 22

The problem involves but simple mathematical concepts like arithmetic operations

http://www.basic-mathematics.com