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 A081975 Triangular number pertaining to A081974. a(n) = A081974(n)*A081974(n+1). 3
 3, 6, 10, 45, 36, 28, 91, 78, 66, 231, 210, 120, 276, 1035, 630, 378, 1431, 1378, 780, 990, 528, 496, 465, 300, 820, 3321, 3240, 2080, 5356, 5253, 1275, 1225, 1176, 1128, 4371, 4278, 4186, 5460, 4560, 11476, 11325, 2775, 666, 2016, 12880, 6555, 1596 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A subset of A000217. - R. J. Mathar, Apr 05 2007 LINKS MAPLE isA000217 := proc(n) local t; t := (sqrt(1+8*n)-1)/2 ; type(t, 'integer'); end: A081974 := proc(nmax) local a, n, prodset; a := [1, 3] ; prodset := {3} ; while nops(a) < nmax do n := 2 ; while n in a or n*op(-1, a) in prodset or isA000217(n*op(-1, a)) = false do n := n+1 ; od ; prodset := prodset union { n*op(-1, a) } ; a := [op(a), n] ; od ; RETURN(a) ; end: A081975 := proc(nmax) local a ; a081974 := A081974(nmax) ; a := [] ; for i from 2 to nops(a081974) do a := [op(a), op(i, a081974)*op(i-1, a081974)] ; od ; RETURN(a) ; end: a := A081975(100) ; # R. J. Mathar, Apr 05 2007 CROSSREFS Cf. A081974, A081976, A081977. Sequence in context: A339783 A317361 A048089 * A160965 A069708 A061455 Adjacent sequences:  A081972 A081973 A081974 * A081976 A081977 A081978 KEYWORD nonn AUTHOR Amarnath Murthy, Apr 03 2003 EXTENSIONS More terms from R. J. Mathar, Apr 05 2007 STATUS approved

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Last modified January 25 15:34 EST 2022. Contains 350572 sequences. (Running on oeis4.)