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1 + Sum[ Prime[k]^(n-1), {k,1,n}].
4

%I #2 Mar 31 2012 13:20:27

%S 2,6,39,504,17765,552552,30870007,1387350084,103306557609,

%T 16762578985600,1290073179870299,216632259853089564,

%U 30312656885388018973,2922170957243151047352,378560698729260507690687

%N 1 + Sum[ Prime[k]^(n-1), {k,1,n}].

%C Prime p divides a(p). n divides a(n) for n={1,2,3,4,5,6,7,9,10,11,12,13,17,19,22,23,29,31,37,41,43,45,47,...}.

%F a(n) = 1 + Sum[ Prime[k]^(n-1), {k,1,n}].

%t Table[1+Sum[Prime[k]^(n-1),{k,1,n}],{n,1,20}]

%K nonn

%O 1,1

%A _Alexander Adamchuk_, Aug 04 2006