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Positions where 2's occur in A056731.
3

%I #4 Mar 30 2012 17:30:26

%S 1,4,8,13,20,28,37,47,59,72,86,101,117,135,154,174,195,217,240,264,

%T 290,317,345,374,404,435,467,500,535,571,608,646,685,725,766,808,851,

%U 896,942,989,1037,1086,1136,1187,1239,1292,1346,1402,1459,1517,1576,1636

%N Positions where 2's occur in A056731.

%F A056738(n) = A005228(n)+A030124(n)-n-1.

%F a(n+1) = a(n) + (n+1) + the number of a(k)'s <= n, 1 <= k <= n and a(1) = 1.

%e a(9) = a(8) + 8 + the number of a(k)'s <= 8 = 47 + 8 + 1 + 3 ( a(3) is <= 8) = 59.

%t f[1] = 1; f[n_] := f[n] = Block[ {k = 1}, While[ f[k] < n, k++ ]; Return[ f[n - 1] + n + k ]]; Table[ f[n], {n, 0, 60} ]

%K nonn,easy

%O 1,2

%A _N. J. A. Sloane_, Aug 31 2000

%E More terms from _Robert G. Wilson v_, Nov 25 2001