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A068628
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Numbers occurring twice in A068627.
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2
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0, 60, 216, 468, 816, 1260, 1800, 2436, 3168, 3996, 4920, 5940, 7056, 8268, 9576, 10980, 12480, 14076, 15768, 17556, 19440, 21420, 23496, 25668, 27936, 30300, 32760, 35316, 37968, 40716, 43560, 46500, 49536, 52668, 55896, 59220, 62640, 66156, 69768, 73476
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OFFSET
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1,2
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COMMENTS
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Recall that A068627 is defined as follows: a(0) = 0, a(n) = a(n-1) + n if n does not divide a(n-1), a(n) = a(n-1) - n if n divides a(n-1), a(n) = n if a(n-1) = 0.
A068627 begins: 0,1,3,0,4,9,15,22,30,39,49,60,48,61,75,60,...
Numbers occurring twice in A068627, like 0, 60 etc. are called nodes.
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LINKS
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PROG
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(PARI) already(val, v, nb)=for (i = 1, nb, if (val == v[i], return (1)); ); return (0);
lista(nn) = {preca = 0; vm = vector(nn); for (n=1, nn, vm[n] = preca; if (preca == 0, nexta = n, if (preca % n, nexta = preca + n, nexta = preca - n); ); if (already(preca, vm, n-1), print1(preca, ", ")); preca = nexta; ); } \\ Michel Marcus, Jan 23 2014
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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Offset changed to 1 and more terms from Michel Marcus, Jan 23 2014
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STATUS
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approved
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