OFFSET
0,3
LINKS
Index entries for linear recurrences with constant coefficients, signature (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, -1).
FORMULA
a(n) = Sum_{i=1..n} (-1)^floor((2*i-2)/19).
a(n) = a(n-1) + a(n-19) - a(n-20) for n > 19.
MATHEMATICA
Table[Sum[(-1)^Floor[(2 i - 2)/19], {i, n}], {n, 0, 100}]
CROSSREFS
Cf. A008611 (one step back, two steps forward).
Cf. A058207 (three steps forward, two steps back).
Cf. A260644 (four steps forward, three steps back).
Cf. A271800 (five steps forward, four steps back).
Cf. A271859 (six steps forward, five steps back).
Cf. A287655 (seven steps forward, six steps back).
Cf. A287793 (eight steps forward, seven steps back).
Cf. A287794 (nine steps forward, eight steps back).
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, May 31 2017
STATUS
approved