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 A126865 a(n) = gcd(Product_{p|n} (p+1)^b(p,n), Product_{p|n} (p-1)^b(p,n)), where the products are over the distinct primes, p, that divide n and p^b(p,n) is the highest power of p dividing n. 2
 1, 1, 2, 1, 2, 2, 2, 1, 4, 2, 2, 2, 2, 6, 8, 1, 2, 4, 2, 2, 4, 2, 2, 2, 4, 6, 8, 6, 2, 8, 2, 1, 4, 2, 24, 4, 2, 6, 8, 2, 2, 12, 2, 2, 16, 2, 2, 2, 4, 4, 8, 6, 2, 8, 8, 6, 4, 2, 2, 8, 2, 6, 8, 1, 12, 4, 2, 2, 4, 24, 2, 4, 2, 6, 16, 18, 12, 24, 2, 2, 16, 2, 2, 12, 4, 6, 8, 2, 2, 16, 8, 2, 4, 2, 24, 2, 2, 12, 8 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS First occurrence of k or 0 if not possible (including all odd primes k): 2, 1, 0, 9, 0, 14, 0, 15, 0, 0, 0, 42, 0, 0, 0, 45, 0, 76, 0, 589, 0, 0, 0, 35, 0, 0, 0, 4381, 0, 0, ..., . - Robert G. Wilson v, Sep 08 2007 LINKS Antti Karttunen, Table of n, a(n) for n = 1..12441 Antti Karttunen, Data supplement: n, a(n) computed for n = 1..100000 FORMULA From Antti Karttunen, Dec 17 2018: (Start) a(n) = gcd(A003958(n), A003959(n)). a(A007947(n)) = A066086(n). (End) EXAMPLE 400 = 2^4 * 5^2. So a(400) = gcd((2+1)^4 * (5+1)^2, (2-1)^4 * (5-1)^2) = gcd(2916, 16) = 4. MATHEMATICA f[n_] := Block[{fi = FactorInteger@n}, GCD[Times @@ ((First /@ fi - 1)^Last /@ fi), Times @@ ((First /@ fi + 1)^Last /@ fi)]]; Array[f, 99] - Robert G. Wilson v, Sep 08 2007 PROG (PARI) A003958(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1]--); factorback(f); }; A003959(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1]++); factorback(f); }; A126865(n) = gcd(A003958(n), A003959(n)); \\ Antti Karttunen, Dec 17 2018 CROSSREFS Cf. A003958, A003959, A066086, A322362. Sequence in context: A167865 A218654 A054571 * A104640 A193335 A016727 Adjacent sequences:  A126862 A126863 A126864 * A126866 A126867 A126868 KEYWORD nonn AUTHOR Leroy Quet, Mar 15 2007 EXTENSIONS More terms from Robert G. Wilson v, Sep 08 2007 STATUS approved

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Last modified December 15 09:05 EST 2019. Contains 329995 sequences. (Running on oeis4.)