OFFSET
1,1
COMMENTS
REFERENCES
J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 399, p. 89, Ellipses, Paris 2008.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..2500
FORMULA
a(n) >= n^2 + 4n + 6. [Charles R Greathouse IV, Dec 13 2011]
EXAMPLE
a(8) = 102 because the prime divisors of 102 are 2, 3 and 17;
(2 + 8) | (102 + 8) = 110 = 10*11;
(3 + 8) | 110 = 11*10.
MAPLE
with(numtheory):for n from 1 to 52 do:i:=0:for k from 1 to 5000 while(i=0) do:x:=factorset(k):n1:=nops(x):y:=k+n: j:=0:for m from 1 to n1 do:if n1>=2 and irem(y, x[m]+n)=0 then j:=j+1:else fi:od:if j>=2 then i:=1:printf(`%d, `, k):else fi:od:od:
MATHEMATICA
numd[n_, k_] := Module[{p=FactorInteger[k][[;; , 1]], c=0}, Do[If[Divisible[n+k, n+p[[i]]], c++], {i, 1, Length[p]}]; c]; a[n_]:=Module[{k=1}, While[numd[n, k] <= 1, k++]; k]; Array[a, 50] (* Amiram Eldar, Sep 09 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Dec 13 2011
STATUS
approved