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A159475 a(1) = 1; for n >= 1, a(n) is the smallest number m > n such that gcd(n,m) > 1. 4

%I

%S 1,4,6,6,10,8,14,10,12,12,22,14,26,16,18,18,34,20,38,22,24,24,46,26,

%T 30,28,30,30,58,32,62,34,36,36,40,38,74,40,42,42,82,44,86,46,48,48,94,

%U 50,56,52,54,54,106,56,60,58,60,60,118,62,122,64,66,66,70,68,134,70,72,72

%N a(1) = 1; for n >= 1, a(n) is the smallest number m > n such that gcd(n,m) > 1.

%C Essentially the same as A061228. [_R. J. Mathar_, Apr 16 2009]

%H Vincenzo Librandi, <a href="/A159475/b159475.txt">Table of n, a(n) for n = 1..10000</a>

%F If n = Product (p_i^e_i), where p_1 < p_2 < ... < p_k, a(n) = n + p_1. For p = primes (A000040), a(p) = 2*p.

%F a(n) = n + A020639(n), for n > 1. - _Michel Marcus_, Dec 02 2018

%t f[n_]:= n + FactorInteger[n][[1, 1]]; Join[{1}, Array[f, 70, 2]] (* _Vincenzo Librandi_, Dec 02 2018 *)

%o (PARI) a(n) = if (n==1, 1, n+factor(n)[1,1]); \\ _Michel Marcus_, Dec 02 2018

%o (MAGMA) [1] cat [n + PrimeDivisors(n)[1]: n in [2..100]]; // _Vincenzo Librandi_, Dec 02 2018

%Y Cf. A000040, A020639, A061228.

%K nonn

%O 1,2

%A _Jaroslav Krizek_, Apr 13 2009

%E More terms from _Michel Marcus_, Dec 02 2018

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Last modified October 17 23:33 EDT 2019. Contains 328135 sequences. (Running on oeis4.)