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 A072492 Values of n for which A072491(n)=3. 1
 27, 35, 51, 57, 65, 77, 87, 93, 95, 117, 119, 121, 122, 123, 125, 135, 143, 145, 147, 148, 155, 161, 171, 177, 185, 187, 189, 190, 203, 205, 207, 208, 209, 215, 217, 219, 220, 221, 237, 245, 247, 249, 250, 255, 261, 267, 275, 287, 289, 291, 292, 297, 299 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Define f(1) = 0. For n>=2, let f(n) = n - p where p is the largest prime <= n. A072491(n) = number of iterations of f to reach 0, starting from n. p+4 is a term if p is a prime but p+2 and p+4 are both composite. LINKS EXAMPLE 27 is a term as f(27)=27-23=4, f(4)=4-3=1 and f(1) = 0. (3 steps.) MATHEMATICA f=0; f[n_] := n-Prime[PrimePi[n]]; a72491[n_] := Module[{k, x}, For[k=0; x=n, x>0, k++; x=f[x], Null]; k]; Select[Range, a72491[ # ]==3&] CROSSREFS Cf. A072491. Sequence in context: A058902 A141550 A032584 * A164376 A025583 A134101 Adjacent sequences:  A072489 A072490 A072491 * A072493 A072494 A072495 KEYWORD nonn,easy AUTHOR Amarnath Murthy, Jul 14 2002 EXTENSIONS Edited by Dean Hickerson, Nov 26 2002 STATUS approved

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Last modified July 2 16:14 EDT 2020. Contains 335404 sequences. (Running on oeis4.)