Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
42	Adding Reversed Numbers	103	84574	6 4
25942	Ball sum	42	1796	11 11
30826	Bernoulli numbers	4	7	23 12
24998	PLAYING WITH BITS	34	791	13 13
36670	Bipartite Permutation	14	364	6 15
17921	XOR	-14	8143	1 1
18294	Problem1	1	81	1 6
26314	Corn Headache	7	357	8 9
34620	Crying Series	2	101	1 4
40400	Count Set Bits		433	1 1
27269	Cube Numbers	29	612	9 11
22403	Divisors of factorial	71	1971	14 14
36267	Fuad the wild scientist		21
27299	Find Log	1	127	1 1
25311	Candies	9	1090	6 7
32445	COUNT JUMPS	1	92	4 1
40512	Kevin likes array	1	48	1 1
25583	Easy Odd Sum	6	1740	4 4
35294	Tricky Means	1	241	17 17
31	Fast Multiplication	48	8997	15 12
16272	Nanoworld	1	39	17 17
25008	New Currency Shopping	1	15	34 17
36963	Nobabs Treasure Hunt	-1	78	1 1
35296	Prime or not Prime!	2	1006	1 6
15708	Divisibility	13	8165	4 3
17104	Fun with Sequences (Act 3)	4	2042	1 1
17126	Fun with Sequences (Act 4)	4	1022	4 1
17481	Fun with Sequences (Act 5)	2	727	1 1
18011	Fun with Sequences (Act 6)	2	1022	1 1
18012	Fun with Sequences (Act 7)		884	1 1
176	Sum of one-sequence	5	670	11 27
22455	SUM OF PRODUCT	35	1064	18 21
35293	Sums to calculate	2	478	1 1
42381	Addition of 2 integers		92
35297	Trial Division	2	130	12 1
235	Very Fast Multiplication	24	1329	26 22

The problem involves but simple mathematical concepts like arithmetic operations

http://www.basic-mathematics.com