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 A171664 Numbers k such that (Product_{d|k} d) - k - 1 and (Product_{d|k} d) + k + 1 are primes. 0
 4, 6, 9, 14, 18, 21, 27, 57, 69, 77, 141, 155, 161, 194, 261, 381, 428, 551, 579, 620, 626, 671, 672, 704, 720, 755, 1007, 1349, 1506, 1529, 1611, 1659, 1707, 1710, 1814, 1982, 1986, 1994, 2036, 2037, 2157, 2429, 2651, 2714, 2771, 2783, 2966, 3039, 3044, 3101 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..50. EXAMPLE Divisors of 6: 1,2,3,6. As 6*3*2*1 = 36, 36 - 6 - 1 = 29 is prime, and 36 + 6 + 1 = 43 is prime, 6 is a term. MATHEMATICA f[n_]:=PrimeQ[Times@@Divisors[n]-n-1]&&PrimeQ[Times@@Divisors[n]+n+1]; lst={}; Do[If[f[n], AppendTo[lst, n]], {n, 7!}]; lst Select[Range[3200], AllTrue[Times@@Divisors[#]+{(#+1), (-#-1)}, PrimeQ]&] (* Harvey P. Dale, Aug 30 2021 *) CROSSREFS Cf. A118369. Sequence in context: A310671 A310672 A310673 * A286303 A084336 A094750 Adjacent sequences: A171661 A171662 A171663 * A171665 A171666 A171667 KEYWORD nonn AUTHOR Vladimir Joseph Stephan Orlovsky, Dec 14 2009 STATUS approved

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Last modified October 2 02:58 EDT 2023. Contains 365831 sequences. (Running on oeis4.)