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A117511
Triangular numbers for which the sum of the digits equals the sum of the digits of the next triangular number.
1
36, 153, 2556, 3240, 4851, 5778, 9045, 11628, 13041, 14535, 17766, 19503, 33930, 41328, 46665, 49455, 52326, 71253, 74691, 81810, 85491, 93096, 109278, 122265, 131328, 140715, 145530, 160461, 170820, 181503, 186966, 192510, 203841, 252405, 258840, 265356
OFFSET
1,1
COMMENTS
s(n) stands for the sum of the digits of n. Each number of the sequence is divisible by 9.
LINKS
FORMULA
s(a(n))=s(a(n+1))
EXAMPLE
153 is in the sequence because (1) 153 is triangular number a(18), triangular number a(19)=171 and (2) 1+5+3=1+7+1
MATHEMATICA
Transpose[With[{c=Partition[Accumulate[Range[2000]], 2, 1]}, Select[c, Total[IntegerDigits[First[#]]]==Total[IntegerDigits[Last[#]]]&]]] [[1]] (* Harvey P. Dale, Oct 18 2011 *)
(#(#+1))/2&/@(SequencePosition[Total[IntegerDigits[#]]&/@Accumulate[ Range[ 1000]], {x_, x_}][[All, 1]]) (* Harvey P. Dale, Mar 02 2022 *)
CROSSREFS
Cf. A000217.
Sequence in context: A034592 A160754 A275496 * A250632 A211728 A211737
KEYWORD
base,nonn
AUTHOR
Luc Stevens (lms022(AT)yahoo.com), Apr 26 2006
EXTENSIONS
Corrected by Harvey P. Dale, Oct 18 2011
STATUS
approved