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a(n) = 5 - (prime(n) mod 10).
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%I #27 Nov 11 2016 21:20:05

%S 3,2,0,-2,4,2,-2,-4,2,-4,4,-2,4,2,-2,2,-4,4,-2,4,2,-4,2,-4,-2,4,2,-2,

%T -4,2,-2,4,-2,-4,-4,4,-2,2,-2,2,-4,4,4,2,-2,-4,4,2,-2,-4,2,-4,4,4,-2,

%U 2,-4,4,-2,4,2,2,-2,4,2,-2,4,-2,-2,-4,2

%N a(n) = 5 - (prime(n) mod 10).

%C Except for a(1)=3 and a(3)=5 the entries are either {-4, -2, 2, 4} and occur in roughly equal ratios. - _Robert G. Wilson v_, Nov 04 2016

%F a(n) = 5 - A007652(n). - _Robert G. Wilson v_, Nov 04 2016

%e For n = 10 and prime(10) = 29, so a(10) = 5 - 9 = -4.

%t f[n_] := 5 - Mod[Prime[n], 10]; Array[f, 71] (* _Robert G. Wilson v_, Nov 04 2016 *)

%o (PARI) a(n) = my(p=prime(n)); (10*(p\10)+5) - p; \\ _Michel Marcus_, Sep 30 2016

%Y Cf. A007652, A184593.

%K sign,easy

%O 1,1

%A _Dimitris Valianatos_, Sep 29 2016