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A238598 Largest integer k such that n >= k^2-k-1 = A165900(k). 1
1, 1, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Also: Truncation to the integer part of the inverse function of A165900 = x -> x^2-x-1 (strictly increasing for x > 1/2): a(n) = floor(g(n)), where g = A165900^{-1}.

A left inverse of A165900 on the positive integers: a(A165900(n)) = n for all n>0.

LINKS

Table of n, a(n) for n=0..86.

FORMULA

a(n) = A000194(n+2) - [n=1], where [P]=1 if P is true, [P]=0 else.

PROG

(PARI) A238598(n)=ceil(sqrtint(4*n+8)/2)-(n==1)

CROSSREFS

Sequence in context: A029836 A004257 A276611 * A156684 A070564 A072358

Adjacent sequences:  A238595 A238596 A238597 * A238599 A238600 A238601

KEYWORD

nonn

AUTHOR

M. F. Hasler, Mar 01 2014

STATUS

approved

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Last modified December 6 18:03 EST 2019. Contains 329809 sequences. (Running on oeis4.)