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 A073613 Triangular numbers which are the sum of two squares. 2
 0, 1, 10, 36, 45, 136, 153, 325, 666, 820, 1225, 1378, 2080, 2628, 2701, 3240, 3321, 4005, 4753, 5050, 6786, 7381, 9316, 10440, 10585, 11026, 14365, 16290, 18721, 19306, 25425, 27028, 27261, 29161, 29890, 32896, 33930, 41616, 41905, 42778 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The squares may be zero. LINKS Robert Israel, Table of n, a(n) for n = 1..10000 FORMULA Intersection of A000217 and A001481. EXAMPLE 0 = A000217(0) = A001481(1) = 0^2 + 0^2 is listed here as a(1). 1 = A000217(1) = A001481(2) = 1^2 + 0^2 is listed here as a(2). 10 = A000217(4) = A001481(8) = 1^2 + 9^2 is listed here as a(3). MAPLE filter:= proc(n)   andmap(t -> (t[1] mod 4 <> 3 or t[2]::even), ifactors(n)[2]) end proc: select(filter, [seq(i*(i+1)/2, i=0..500)]); # Robert Israel, Nov 22 2017 MATHEMATICA t = Range[0, 250]^2; t1 = Flatten[Table[a + b, {a, t}, {b, t}]]; t2 = Accumulate[Range[300]]; Intersection[t1, t2] (* Jayanta Basu, Jul 03 2013 *) Select[Union[Total/@Tuples[Range[0, 300]^2, 2]], OddQ[Sqrt[8#+1]]&] (* Harvey P. Dale, Apr 22 2015 *) PROG (PARI) is_A073613(n)=is_A000217(n)&&is_A001481(n) \\ M. F. Hasler, Nov 20 2017 CROSSREFS Cf. A000217 (triangular numbers), A001481 (sums of two squares). Sequence in context: A343155 A223305 A176575 * A117404 A309783 A072517 Adjacent sequences:  A073610 A073611 A073612 * A073614 A073615 A073616 KEYWORD easy,nonn AUTHOR Jason Earls, Aug 29 2002 EXTENSIONS Edited and initial 0 added by M. F. Hasler, Nov 20 2017 STATUS approved

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Last modified June 15 22:06 EDT 2021. Contains 345053 sequences. (Running on oeis4.)