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 A233400 Number n such that a2 - n^3 is a triangular number (A000217), where a2 is the least square above n^3. 2
 0, 1, 2, 9, 12, 107, 109, 120, 244, 337, 381, 407, 565, 592, 937, 1209, 1224, 1341, 1717, 2032, 2402, 3280, 4957, 5149, 5265, 5644, 7065, 7240, 8181, 8820, 9712, 10732, 11901, 15059, 18300, 19120, 20436, 22672, 24516, 25139, 28044, 28550, 36145, 38221, 66201, 72335, 77100 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The sequence of cubes begins: 0, 1, 8, 729, 1728, 1225043, 1295029, 1728000, 14526784, 38272753, 55306341, ... The sequence of squares begins: 1, 4, 9, 784, 1764, 1225449, 1295044, 1729225, 14531344, 38278969, 55308969, ... The sequence of roots of these squares begins: 1, 2, 3, 28, 42, 1107, 1138, 1315, 3812, 6187, 7437, 8211, 13430, 14404, 28682, ... LINKS PROG (Python) def isqrt(a): sr = 1L << (long.bit_length(long(a)) >> 1) while a < sr*sr: sr>>=1 b = sr>>1 while b: s = sr+b if a >= s*s: sr = s b>>=1 return sr def isTriangular(a): a+=a sr = isqrt(a) return (a==sr*(sr+1)) for n in range(77777): n3 = n*n*n a = isqrt(n3)+1 if isTriangular(a*a-n3): print str(n)+', ', CROSSREFS Cf. A000217, A000290, A000578, A233401. Sequence in context: A125019 A259984 A225548 * A234945 A357729 A271646 Adjacent sequences: A233397 A233398 A233399 * A233401 A233402 A233403 KEYWORD nonn AUTHOR Alex Ratushnyak, Dec 09 2013 STATUS approved

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Last modified April 2 02:09 EDT 2023. Contains 361723 sequences. (Running on oeis4.)