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A224912
Numbers m for which Sum_{i=1..k} (p(i)/(p(i)-1)) + Product_{i=1..k} (p(i)/(p(i)-1)) is an integer, where p(i) are the k prime factors of m (with multiplicity).
4
2, 3, 4, 8, 16, 32, 36, 64, 72, 108, 128, 144, 200, 256, 288, 396, 512, 528, 576, 588, 1024, 1040, 1152, 1296, 2000, 2048, 2304, 2320, 2400, 2592, 3888, 4096, 4160, 4608, 4752, 4800, 5184, 5600, 6552, 7200, 8192, 8448, 9216, 9600, 9936, 10368, 11316, 12000
OFFSET
1,1
COMMENTS
Apart from 3 all terms are even.
LINKS
EXAMPLE
Prime factors of 11316 are 2^2, 3, 23 and 41.
Sum_{i=1..5} (p(i)/(p(i)-1)) = 2*(2/(2-1)) + 3/(3-1) + 23/(23-1) + 41/(41-1) = 3331/440.
Sroduct_{i=1..5} (p(i)/(p(i)-1)) = 2*(2/(2-1)) * 3/(3-1) * 23/(23-1) * 41/(41-1) = 2829/440.
Their sum is an integer: 3331/440 + 2829/440 = 14.
MAPLE
with(numtheory);
A224912:=proc(i) local b, c, d, n, p;
for n from 2 to i do p:=ifactors(n)[2];
b:=add(op(2, d)*op(1, d)/(op(1, d)-1), d=p)+mul((op(1, d)/(op(1, d)-1))^op(2, d), d=p);
if trunc(b)=b then print(n); fi; od; end:
A224912(10^6);
CROSSREFS
Sequence in context: A118841 A126294 A339973 * A162724 A244750 A140974
KEYWORD
nonn
AUTHOR
Paolo P. Lava, Apr 19 2013
STATUS
approved