Sphere Online Judge (SPOJ)

ID	NAME	QUALITY	USERS	DIFFICULTY C I
42	Adding Reversed Numbers	103	79630	6 4
25942	Ball sum	42	1788	11 11
30826	Bernoulli numbers	4	7	23 12
24998	PLAYING WITH BITS	34	784	13 13
36670	Bipartite Permutation	14	357	6 15
17921	XOR	-14	7902	1 1
18294	Problem1	1	75	1 6
26314	Corn Headache	7	356	8 9
34620	Crying Series	2	92	1 4
40400	Count Set Bits		405	1 1
27269	Cube Numbers	29	606	9 11
22403	Divisors of factorial	71	1933	14 14
36267	Fuad the wild scientist		11
27299	Find Log	1	125	1 1
25311	Candies	9	1087	6 7
32445	COUNT JUMPS	1	90	4 1
40512	Kevin likes array	1	47	1 1
25583	Easy Odd Sum	6	1715	4 4
35294	Tricky Means	1	228	17 17
31	Fast Multiplication	48	8895	15 12
16272	Nanoworld	1	38	17 17
25008	New Currency Shopping	1	11	34 17
36963	Nobabs Treasure Hunt	-1	72	1 1
35296	Prime or not Prime!	2	862	1 6
15708	Divisibility	13	7908	4 3
17104	Fun with Sequences (Act 3)	4	2005	1 1
17126	Fun with Sequences (Act 4)	4	1013	4 1
17481	Fun with Sequences (Act 5)	2	719	1 1
18011	Fun with Sequences (Act 6)	2	1011	1 1
18012	Fun with Sequences (Act 7)		876	1 1
176	Sum of one-sequence	5	666	11 27
22455	SUM OF PRODUCT	34	1053	18 20
35293	Sums to calculate	2	455	1 1
42381	Addition of 2 integers		46
35297	Trial Division	2	118	12 1
235	Very Fast Multiplication	24	1286	26 22

The problem involves but simple mathematical concepts like arithmetic operations

http://www.basic-mathematics.com