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 A262242 Triangular numbers representable as 2^x + 2^y. 3
 3, 6, 10, 36, 66, 136, 528, 2080, 8256, 32896, 131328, 524800, 2098176, 8390656, 33558528, 134225920, 536887296, 2147516416, 8590000128, 34359869440, 137439215616, 549756338176, 2199024304128, 8796095119360, 35184376283136, 140737496743936, 562949970198528 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Chai Wah Wu, Table of n, a(n) for n = 1..502 FORMULA Conjectures from Colin Barker, Sep 16 2015: (Start) a(n) = 2^(n-5)*(2^n+4) for n>5. a(n) = 6*a(n-1)-8*a(n-2) for n>7. G.f.: x*(240*x^6+28*x^5-70*x^4+24*x^3-2*x^2-12*x+3) / ((2*x-1)*(4*x-1)). (End) PROG (Python) def isTriangular(a): sr = 1 << (int.bit_length(a) >> 1) a += a while a < sr*(sr+1): sr>>=1 b = sr>>1 while b: s = sr+b if a >= s*(s+1): sr = s b>>=1 return (a==sr*(sr+1)) for a in range(1, 200): for b in range(a): c = (1<

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Last modified December 4 23:46 EST 2022. Contains 358572 sequences. (Running on oeis4.)