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A230775 Smallest prime number greater than or equal to the square root of n. 2
2, 2, 2, 2, 3, 3, 3, 3, 3, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Or repeat prime(k) (prime(k)^2-prime(k-1)^2) times, with prime(0) set to 0 for k=1.

LINKS

Jean-Christophe Hervé, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A000040(A230774(n)).

Repeat prime(1) prime(1)^2 times; for k>1, repeat A000040(k) A050216(k-1) times (that is, repeat prime(k) (prime(k)^2 - prime(k-1)^2) times).

EXAMPLE

a(5)=a(6)=a(7)=a(8)=a(9)=3 because prime(1)= 2 < sqrt(5 to 9) <= prime(2) = 3.

MATHEMATICA

spn[n_]:=Module[{s=Sqrt[n]}, If[PrimeQ[s], s, NextPrime[s]]]; Array[spn, 90] (* Harvey P. Dale, Feb 10 2019 *)

CROSSREFS

Cf. A230774, A050216, A056813.

Sequence in context: A135297 A176146 A171481 * A108037 A237354 A261104

Adjacent sequences:  A230772 A230773 A230774 * A230776 A230777 A230778

KEYWORD

nonn,easy

AUTHOR

Jean-Christophe Hervé, Nov 01 2013

STATUS

approved

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Last modified September 23 11:24 EDT 2021. Contains 347612 sequences. (Running on oeis4.)