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A047331
Numbers that are congruent to {2, 3, 5, 6} mod 7.
1
2, 3, 5, 6, 9, 10, 12, 13, 16, 17, 19, 20, 23, 24, 26, 27, 30, 31, 33, 34, 37, 38, 40, 41, 44, 45, 47, 48, 51, 52, 54, 55, 58, 59, 61, 62, 65, 66, 68, 69, 72, 73, 75, 76, 79, 80, 82, 83, 86, 87, 89, 90, 93, 94, 96, 97, 100, 101, 103, 104, 107, 108, 110, 111
OFFSET
1,1
FORMULA
G.f.: x*(2+x+2*x^2+x^3+x^4) / ( (1+x)*(1+x^2)*(x-1)^2 ). - R. J. Mathar, Dec 04 2011
From Wesley Ivan Hurt, Jun 03 2016: (Start)
a(n) = a(n-1) + a(n-4) - a(n-5) for n>5.
a(n) = (14*n-3-3*i^(2*n)-(1-i)*i^(-n)-(1+i)*i^n)/8 where i=sqrt(-1).
a(2k) = A047280(k), a(2k-1) = A047385(k). (End)
MAPLE
A047331:=n->(14*n-3-3*I^(2*n)-(1-I)*I^(-n)-(1+I)*I^n)/8: seq(A047331(n), n=1..100); # Wesley Ivan Hurt, Jun 03 2016
MATHEMATICA
Table[(14n-3-3*I^(2n)-(1-I)*I^(-n)-(1+I)*I^n)/8, {n, 80}] (* Wesley Ivan Hurt, Jun 03 2016 *)
PROG
(Magma) [n : n in [0..150] | n mod 7 in [2, 3, 5, 6]]; // Wesley Ivan Hurt, Jun 03 2016
CROSSREFS
Sequence in context: A024620 A232527 A188375 * A288480 A344633 A029451
KEYWORD
nonn,easy
STATUS
approved