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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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Paolo P. Lava, Table of n, a(n) for n = 1..100 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 Cf. A208728, A225702-A225704, A225706-A225720. Sequence in context: A223363 A284440 A020248 * A259758 A203173 A194532 Adjacent sequences:  A225702 A225703 A225704 * A225706 A225707 A225708 KEYWORD nonn AUTHOR Paolo P. Lava, May 13 2013 STATUS approved

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Last modified June 19 21:19 EDT 2021. Contains 345151 sequences. (Running on oeis4.)