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 A180039 Combinatorial tetrahedral numbers 1
 1, 112, 111223, 1111222334, 111112222333445, 111111222223333444556, 1111111222222333334444555667, 111111112222222333333444445555666778, 111111111222222223333333444444555556666777889 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS These are partial sums in adding base-1 triangular numbers (1 + 111 + 111111 + 1111111111,...). Third row of: 1,2,3,4,5,... 1,12,123,1234,12345,... 1,112,111223,1111222334,111112222333445,... 1,1112,1111112223,11111111112222223334,11111111111111122222222223333334445,.. LINKS FORMULA a(n) = Sum_{i=1..n} A002275(A000217(i)). - R. J. Mathar, Nov 02 2016 EXAMPLE For n=4, a(4)= 1 + 111 + 111111 + 1111111111 = 1111222334. Combinatorially: 1,12,123,1234,12345,123456,... 1,21,321,4321,54321,654321,... ----------------------------- X 1,112,111223,1111222334....... For n =(4),a(4)= 4 x 1 + 3 x 2 + 2 x 3 + 1 x 4 = 1111 + 222 + 33 + 4 = 1111222334. CROSSREFS Cf. A000292, A014824, A180027. Sequence in context: A184898 A270113 A275052 * A261949 A159432 A151645 Adjacent sequences:  A180036 A180037 A180038 * A180040 A180041 A180042 KEYWORD nonn,easy,base AUTHOR Mark Dols, Aug 07 2010 STATUS approved

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Last modified September 29 10:03 EDT 2020. Contains 337428 sequences. (Running on oeis4.)