A007604 a(n) = a(n-1) + a(n-1-(number of odd terms so far)). (Formerly M0567)

1, 2, 3, 4, 6, 9, 12, 16, 22, 31, 40, 52, 68, 90, 121, 152, 192, 244, 312, 402, 523, 644, 796, 988, 1232, 1544, 1946, 2469, 2992, 3636, 4432, 5420, 6652, 8196, 10142, 12611, 15080, 18072, 21708, 26140, 31560, 38212, 46408, 56550, 69161, 81772, 96852

Offset

1,2

Comments

A003056(n) gives the number of odd terms in the first n terms of this sequence. Modulo 2, this sequence becomes A023531. - T. D. Noe, Jul 24 2007

The present definition was the original definition of this sequence. It was later changed to "Sequence formed from rows of triangle A046936", but this seems less satisfactory. - N. J. A. Sloane, Oct 26 2014

References

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

T. D. Noe, Table of n, a(n) for n = 1..1000

Maple

A[1]:= 1: A[2]:= 2: o:= 1:
for n from 3 to 100 do
  A[n]:= A[n-1] + A[n-1-o];
  if A[n]::odd then o:= o+1 fi
od:
seq(A[i], i=1..100); # Robert Israel, Mar 14 2023

Mathematica

a[n_Integer] := a[n] = Block[{c, k}, c = 0; k = 1; While[k < n, If[ OddQ[ a[k] ], c++ ]; k++ ]; Return[a[n - 1] + a[n - 1 - c] ] ]; a[1] = 1; a[2] = 2; Table[ a[n], {n, 0, 60} ]

Prog

(Haskell)
a007604 n = a007604_list !! (n-1)
a007604_list = concat $ map tail $ tail a046936_tabl
-- Reinhard Zumkeller, Jan 01 2014

Crossrefs

Cf. A006336, A046936, A003056.

Sequence in context: A083365 A001935 A286141 * A013950 A350842 A018550

Adjacent sequences: A007601 A007602 A007603 * A007605 A007606 A007607

Keyword

nonn,nice,easy

Author

N. J. A. Sloane, Robert G. Wilson v

Extensions

Entry revised by N. J. A. Sloane, Oct 26 2014

Status

approved