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

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

Author

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

Keywords

• nonn
• nice
• easy

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

Crossrefs

Cf. A006336, A046936, A003056.

Programs

Haskell

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

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} ]

Extensions

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