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 A218273 Square triangular numbers that can be expressed as sums of a positive square number and a positive triangular number. Intersection of A182427 and A214937. 0
 1225, 1413721, 48024900, 1631432881, 1882672131025, 63955431761796, 2172602007770041, 73804512832419600, 85170343853180456676, 2893284510173841030625, 98286503002057414584576, 3338847817559778254844961, 113422539294030403250144100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Theorem (I. N. Ianakiev): There are infinitely many such numbers. Proof: Any A001110(2n+1), for n>0, is such a number as A001110(2n+1) = (2a+1)^2+(4a^2+4a)(4a^2+4a+1)(1/2), where a = (A002315(n)-1)(1/2). Note: other numbers, not of the form A001110(2n+1), e.g. A001110(6), are also in the sequence (see the example below). Every term is divisible by its digital root (A010888). - Ivan N. Ianakiev, Oct 17 2013 LINKS EXAMPLE a(3) = A001110(6) = 48024900 = 6918^2 + [576*577*(1/2)]. CROSSREFS Cf. A000217, A000290, A001110, A182427, A214937. Sequence in context: A014795 A267297 A151657 * A046177 A031748 A031658 Adjacent sequences:  A218270 A218271 A218272 * A218274 A218275 A218276 KEYWORD nonn,more AUTHOR Ivan N. Ianakiev, Oct 25 2012 EXTENSIONS a(8)-a(13) from Donovan Johnson, Nov 02 2012 STATUS approved

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Last modified July 8 03:25 EDT 2020. Contains 335503 sequences. (Running on oeis4.)