OFFSET
1,3
COMMENTS
Sequence B is called a reluctant sequence of sequence A, if B is triangle array read by rows: row number k coincides with first k elements of the sequence A. Sequence A122507 is the reluctant sequence of A018805. - Boris Putievskiy, Dec 14 2012
LINKS
Boris Putievskiy, Transformations Integer Sequences And Pairing Functions, arXiv:1212.2732 [math.CO], 2012.
FORMULA
a(n) = A018805(m), where m = n-t(t+1)/2, t = floor((-1+sqrt(8*n-7))/2). - Boris Putievskiy, Dec 14 2012
EXAMPLE
1
1, 3
1, 3, 7
1, 3, 7, 11
1, 3, 7, 11, 19
1, 3, 7, 11, 19, 23
MATHEMATICA
a1 = Table[ FoldList[ Plus, 1, 2 Array[ EulerPhi, n, 2 ] ], {n, 0, 10}] Flatten[a1]
Module[{nn=20, ep}, ep=Accumulate[2*EulerPhi[Range[nn]]]-1; Table[Take[ep, n], {n, nn}]]// Flatten (* Harvey P. Dale, May 24 2023 *)
CROSSREFS
KEYWORD
nonn,tabl
AUTHOR
Roger L. Bagula, Sep 15 2006
EXTENSIONS
Edited by N. J. A. Sloane, Jun 16 2007
STATUS
approved