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 A078701 Least odd prime factor of n, or 1 if no such factor exists. 23
 1, 1, 3, 1, 5, 3, 7, 1, 3, 5, 11, 3, 13, 7, 3, 1, 17, 3, 19, 5, 3, 11, 23, 3, 5, 13, 3, 7, 29, 3, 31, 1, 3, 17, 5, 3, 37, 19, 3, 5, 41, 3, 43, 11, 3, 23, 47, 3, 7, 5, 3, 13, 53, 3, 5, 7, 3, 29, 59, 3, 61, 31, 3, 1, 5, 3, 67, 17, 3, 5, 71, 3, 73, 37, 3, 19, 7, 3, 79, 5, 3, 41, 83, 3, 5, 43, 3, 11 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 FORMULA a(n) = A020639(A000265(n)); a(n) = A020639(n) iff n is odd; a(2^k) = 1. MAPLE A078701 := proc(n) fs := numtheory[factorset](n) minus {2}; if fs = {} then 1; else min(op(fs)) ; end if; end proc: # R. J. Mathar, Feb 06 2019 MATHEMATICA lof[n_]:=Module[{fac=Select[Transpose[FactorInteger[n]][[1]], OddQ]}, If[fac=={}, 1, Min[fac]]]; Array[lof, 90] (* Harvey P. Dale, Apr 14 2012 *) a[n_] := FactorInteger[n/2^IntegerExponent[n, 2]][[1, 1]]; Array[a, 100] (* Amiram Eldar, Jul 04 2022 *) PROG (Haskell) a078701 n = if null odds then 1 else head odds where odds = tail \$ a182469_row n -- Reinhard Zumkeller, Oct 08 2012 (PARI) a(n) = my(v = select(x->((x%2)==1), factor(n)[, 1])); if (#v, vecmin(v), 1); \\ Michel Marcus, Oct 25 2017 (PARI) A078701(n)=iferr(factor(n)[2-bittest(n, 0), 1], E, 1) \\ M. F. Hasler, Nov 06 2017 (Python) from sympy import factorint def A078701(n): return min((p for p in factorint(n) if p > 2), default=1) # Chai Wah Wu, Feb 03 2022 CROSSREFS Cf. A000265, A020639, A005408, A000079. Sequence in context: A308655 A356365 A217663 * A299766 A161398 A204455 Adjacent sequences: A078698 A078699 A078700 * A078702 A078703 A078704 KEYWORD nonn AUTHOR Reinhard Zumkeller, Dec 18 2002 STATUS approved

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Last modified April 21 14:30 EDT 2024. Contains 371874 sequences. (Running on oeis4.)