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A225705
Composite squarefree numbers n such that p(i)-5 divides n+5, where p(i) are the prime factors of n.
3
21, 91, 187, 391, 3451, 4147, 6391, 7579, 8827, 9499, 9823, 11803, 15283, 21307, 22243, 26887, 29563, 36091, 42763, 49387, 62491, 63427, 84091, 89947, 107707, 116083, 126451, 139867, 155227, 227263, 270391, 287419, 302731, 317191, 320827, 376987, 381667, 433939
OFFSET
1,1
LINKS
EXAMPLE
Prime factors of 6391 are 7, 11 and 83. We have that (6391+5)/(7-5) =3198, (6391+5)/(11-5) = 1066 and (6391+5)/(83-5) = 82.
MAPLE
with(numtheory); A225705:=proc(i, j) local c, d, n, ok, p, t;
for n from 1 to i do if not isprime(n) then p:=ifactors(n)[2]; ok:=1;
for d from 1 to nops(p) do if p[d][2]>1 or p[d][1]=j then ok:=0; break; fi;
if not type((n+j)/(p[d][1]-j), integer) then ok:=0; break; fi; od;
if ok=1 then print(n); fi; fi; od; end: A225705(10^9, 5);
MATHEMATICA
t = {}; n = 0; While[Length[t] < 50, n++; {p, e} = Transpose[FactorInteger[n]]; If[Length[p] > 1 && Union[e] == {1} && Mod[n, 5] > 0 && Union[Mod[n + 5, p - 5]] == {0}, AppendTo[t, n]]]; t (* T. D. Noe, May 17 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paolo P. Lava, May 13 2013
STATUS
approved