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Replace 2n+1 with concatenation of its nontrivial divisors.
0

%I #9 Mar 31 2017 22:40:07

%S 0,0,0,0,3,0,0,35,0,0,37,0,5,39,0,0,311,57,0,313,0,0,35915,0,7,317,0,

%T 511,319,0,0,37921,513,0,323,0,0,351525,711,0,3927,0,517,329,0,713,

%U 331,519,0,391133,0,0,357152135,0,0,337,0,523,391339,717,11,341,525,0,343,0

%N Replace 2n+1 with concatenation of its nontrivial divisors.

%e Divisors of 15 are 1,3,5,15, so a(7)=35

%t Join[{0},Table[FromDigits[Flatten[IntegerDigits/@Most[Rest[ Divisors[ 2n+1]]]]],{n,70}]] (* _Harvey P. Dale_, Nov 17 2014 *)

%K nonn,base,easy

%O 0,5

%A _N. J. A. Sloane_

%E More terms from _Erich Friedman_