A068628 Numbers occurring twice in A068627.

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

Offset: 1

Author

Amarnath Murthy, Feb 26 2002

Keywords

• easy
• nonn

Comments

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.

Links

• Index entries for linear recurrences with constant coefficients, signature (3,-3,1).

Programs

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

Extensions

Name and comments edited by Michel Marcus, Jan 23 2014

Offset changed to 1 and more terms from Michel Marcus, Jan 23 2014