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%I #34 Jan 23 2020 02:51:13
%S 1,1,10,1,6,1,10,1,7,16,5,1,3,2,10,1,14,1,10
%N k is the first integer such that phi(k+n) | sigma(k)+n.
%C a(20)=12, a(21)=98, a(22)=26, a(23)=1, a(24)=15, a(25)=8. - _Jud McCranie_, Jan 19 2020
%C a(19) > 10^13, if it exists. - _Giovanni Resta_, Jan 23 2020
%e For n=6, a(6)=10 because phi(10+6)=8 which divides sigma(10)+6=24, and k=10 is the smallest integer with that property. - _Jud McCranie_, Jan 19 2020
%o (PARI) a(n) = k=1; while ((sigma(k)+n) % eulerphi(k+n), k++); k; \\ _Michel Marcus_, Feb 03 2014
%K nonn,more,hard
%O 0,3
%A _Robert G. Wilson v_
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