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a(n) = (A001414(prime(n)-1)*A001414(prime(n)+1)) mod prime(n).
2

%I #9 Dec 01 2020 11:35:04

%S 0,2,0,2,5,11,13,15,2,23,7,25,9,8,40,28,18,30,1,26,30,76,21,43,14,5,6,

%T 73,16,21,83,98,96,31,19,73,50,141,24,41,112,149,8,134,145,105,125,45,

%U 39,93,36,177,143,38,254,30,60,129,75,93,221,291,243,214,55,59,172,167,54,335,285,205

%N a(n) = (A001414(prime(n)-1)*A001414(prime(n)+1)) mod prime(n).

%C a(n)=1 for n=19 and 7476. Are there others?

%H Robert Israel, <a href="/A339327/b339327.txt">Table of n, a(n) for n = 1..10000</a>

%e a(4) = (A001414(6)*A001414(8)) mod 7 = (5*6) mod 7 = 2.

%p spf:= proc(n) add(t[1]*t[2],t=ifactors(n)[2]) end proc:

%p f:= proc(n) local p;

%p p:= ithprime(n);

%p spf(p-1)*spf(p+1) mod p

%p end proc:

%p map(f, [$1..100]);

%Y Cf. A001414.

%K nonn,look

%O 1,2

%A _J. M. Bergot_ and _Robert Israel_, Nov 30 2020