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 A055235 Sums of two powers of 3. 12
 2, 4, 6, 10, 12, 18, 28, 30, 36, 54, 82, 84, 90, 108, 162, 244, 246, 252, 270, 324, 486, 730, 732, 738, 756, 810, 972, 1458, 2188, 2190, 2196, 2214, 2268, 2430, 2916, 4374, 6562, 6564, 6570, 6588, 6642, 6804, 7290, 8748, 13122, 19684, 19686, 19692, 19710 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS T. D. Noe, Rows n = 0..100 of triangle, flattened FORMULA a(n+1) = 3^(n-trinv(n)*(trinv(n)+1)/2)+3^trinv(n), where trinv(n) = floor((sqrt(1+8*n)-1)/2) = A003056(n) and n-trinv(n)*(trinv(n)+1)/2 = A002262(n). [corrected by M. F. Hasler, Oct 08 2011] Regarded as a triangle, T(n, k) = 3^n + 3^k, because 3^n + 3^n < 3^(n+1) + 3^0 for all n > 0. MATHEMATICA mx = 10; Sort[Flatten[Table[3^x + 3^y, {y, 0, mx}, {x, 0, y}]]] (* Vladimir Joseph Stephan Orlovsky, Apr 20 2011 *) f[n_] := Block[{t = Floor[(Sqrt[1 + 8 (n - 1)] - 1)/2]}, 3^(n - 1 - t*(t + 1)/2) + 3^t]; Array[f, 49] (* Robert G. Wilson v, Oct 08 2011 *) PROG (PARI) for( n=0, 5, for(k=0, n, print1(3^n+3^k", "))) (PARI) A055235(n)={ my( t=(sqrtint(8*n-7)-1)\2); 3^t+3^(n-1-t*(t+1)/2) }  \\ M. F. Hasler, Oct 08 2011 CROSSREFS Cf. A052216. Sequence in context: A065385 A244052 A324059 * A083887 A339736 A064374 Adjacent sequences:  A055232 A055233 A055234 * A055236 A055237 A055238 KEYWORD easy,nonn,tabl AUTHOR Henry Bottomley, Jun 22 2000 STATUS approved

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Last modified December 7 13:08 EST 2021. Contains 349581 sequences. (Running on oeis4.)