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 A076712 Triangular numbers which are also happy numbers (cf. A007770). 1
 1, 10, 28, 91, 190, 496, 820, 946, 1128, 1275, 2080, 2211, 2485, 3321, 4278, 8128, 8256, 8778, 9591, 9730, 11476, 12090, 12880, 13203, 13366, 13530, 15753, 16471, 17205, 17578, 20910, 21115, 21321, 22791, 24753, 25651, 27261, 29890, 30135 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Donovan Johnson, Table of n, a(n) for n = 1..1000 Shyam Sunder Gupta Fascinating Triangular Numbers EXAMPLE a(4)=91: 91 is a triangular number and also a happy number as 9^2+1^2=82, 8^2+2^2=68, 6^2+8^2=100 and 1^2+0^2+0^2=1. So 91 is triangular happy number. MATHEMATICA Module[{nn=300, trnos, haps}, trnos=Accumulate[Range[nn]]; haps=Select[Range[ (nn(nn+1))/2], FixedPoint[ Total[IntegerDigits[#]^2]&, #, 10]==1&]; Intersection[ trnos, haps]] (* Harvey P. Dale, Aug 15 2014 *) CROSSREFS Cf. A007770. Sequence in context: A124703 A251319 A126364 * A116973 A264579 A003665 Adjacent sequences:  A076709 A076710 A076711 * A076713 A076714 A076715 KEYWORD nonn,base AUTHOR Shyam Sunder Gupta, Oct 26 2002 STATUS approved

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Last modified October 23 17:32 EDT 2019. Contains 328373 sequences. (Running on oeis4.)