A014368 - OEIS

A014368

a(n) = bc, where n = C(b,2)+C(c,1), b>c>=0.

20, 21, 30, 31, 32, 40, 41, 42, 43, 50, 51, 52, 53, 54, 60, 61, 62, 63, 64, 65, 70, 71, 72, 73, 74, 75, 76, 80, 81, 82, 83, 84, 85, 86, 87, 90, 91, 92, 93, 94, 95, 96, 97, 98, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 1110, 120, 121, 122, 123

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OFFSET

1,1

COMMENTS

The definition means: write n as the highest possible triangular number plus some nonnegative rest (so b is one plus the index of the greedy inverse of n in A000217), and concatenate the two decimal expansions of b and the rest. - R. J. Mathar, May 25 2023

REFERENCES

W. Bruns and J. Herzog, Cohen-Macaulay Rings, Cambridge, 1993, p. 158.

LINKS

Table of n, a(n) for n=1..69.

MAPLE

invA000217 := proc(n)

local i;

for i from 1 do

if binomial(i+1, 2) > n then

return i;

end if;

end do:

end proc:

A014368 := proc(n)

local b, c;

b := invA000217(n) ;

c := n-binomial(b, 2) ;

digcatL([b, c]) ;

end proc:

seq(A014368(n), n=1..70) ; # R. J. Mathar, May 25 2023

CROSSREFS

Sequence in context: A218539 A295488 A008940 * A308238 A118865 A118608

Adjacent sequences: A014365 A014366 A014367 * A014369 A014370 A014371

KEYWORD

nonn,easy,base

AUTHOR

N. J. A. Sloane.

STATUS

approved