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 A232608 Triangular numbers t such that distances from t to three nearest squares are three triangular numbers. 2
 1, 10, 15, 253, 325, 11026, 237016, 8439886, 1119946128 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Triangular numbers in A232501. LINKS Table of n, a(n) for n=1..9. PROG (C99) #include #include typedef unsigned long long U64; int isTriang(U64 x) { x+=x; U64 r = sqrt(x); return (r*(r+1)==x); } int main() { for (U64 n=0, i=0; i < (1ULL<<32); ++i) { U64 s, d, d1, d2, d3; s = sqrt(n+=i); d1 = n - s*s; if (!isTriang(d1)) continue; d2 = (s+1)*(s+1) - n; if (!isTriang(d2)) continue; d3 = (s+2)*(s+2) - n; if (s) { d = n - (s-1)*(s-1); if (d < d3) d3 = d; } if (isTriang(d3)) printf("%llu, ", n); } } (Haskell) a232608 n = a232608_list !! (n-1) a232608_list = filter f \$ tail a000217_list where f x = all ((== 1) . a010054) \$ init \$ sort \$ map (abs . (x -) . (^ 2) . (+ (a000196 x))) [-1..2] -- Reinhard Zumkeller, Mar 16 2014 CROSSREFS Cf. A000217, A000290, A232501. Cf. A000196, A010054. Sequence in context: A278349 A114703 A134515 * A175335 A167788 A341012 Adjacent sequences: A232605 A232606 A232607 * A232609 A232610 A232611 KEYWORD nonn,hard,more AUTHOR Alex Ratushnyak, Feb 23 2014 STATUS approved

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Last modified December 2 04:17 EST 2023. Contains 367506 sequences. (Running on oeis4.)