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This sequence and A139143 are complements. a(1) = 1, A139143(1) = 2, a(n+1) = a(n) + Sum_{k = 1..n} A139143(k).
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%I #11 Feb 08 2019 12:08:47

%S 1,3,9,20,37,61,93,135,188,253,331,423,530,653,793,951,1128,1326,1546,

%T 1789,2056,2348,2666,3011,3384,3786,4218,4681,5176,5704,6266,6863,

%U 7496,8167,8877,9627,10418,11251,12127,13047,14012,15023,16081,17187,18342,19547

%N This sequence and A139143 are complements. a(1) = 1, A139143(1) = 2, a(n+1) = a(n) + Sum_{k = 1..n} A139143(k).

%C A139143 consists of all positive integers not in A139142 and vice versa.

%H Rémy Sigrist, <a href="/A139142/b139142.txt">Table of n, a(n) for n = 1..10000</a>

%H Rémy Sigrist, <a href="/A139142/a139142.gp.txt">PARI program for A139142</a>

%e A specific example: a(5) = a(4) + Sum_{k = 1..4} A139143(k) = 20 + 2 + 4 + 5 + 6 = 37.

%o (PARI) See Links section.

%Y Cf. A139143.

%K nonn

%O 1,2

%A _Leroy Quet_, Apr 10 2008

%E More terms from _Rémy Sigrist_, Feb 08 2019