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A245508

Smallest double square (cf. A001105) greater than n-th prime.

2, 8, 8, 8, 18, 18, 18, 32, 32, 32, 32, 50, 50, 50, 50, 72, 72, 72, 72, 72, 98, 98, 98, 98, 98, 128, 128, 128, 128, 128, 128, 162, 162, 162, 162, 162, 162, 200, 200, 200, 200, 200, 200, 200, 200, 200, 242, 242, 242, 242, 242, 242, 242, 288, 288, 288, 288

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OFFSET

1,1

COMMENTS

For n > 2: prime(n) < a(n) < 2*prime(n) and a(n) = A245499(A000040(n),2).

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

MATHEMATICA

Module[{nn=60, ds}, ds=2 Range[0, Ceiling[Sqrt[Prime[nn]]]]^2; Join[ {2}, Table[ SelectFirst[ds, #>Prime[n]&], {n, 2, nn}]]] (* Harvey P. Dale, Jan 07 2020 *)

PROG

(Haskell)

import Data.List (genericIndex)

a245508 n = genericIndex a245508_list (n-1)

a245508_list = f a000040_list a001105_list where

f ps'@ (p:ps) xs'@(x:xs) = if p <= x then x : f ps xs' else f ps' xs

(PARI) a(n) = my(k=prime(n)+(n!=1)); while (! issquare(k/2), k+=2); k; \\ Michel Marcus, Jan 24 2022

CROSSREFS

Cf. A000040, A001105, A145445.

Sequence in context: A284781 A289841 A143812 * A193639 A388370 A154481

Adjacent sequences: A245505 A245506 A245507 * A245509 A245510 A245511

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Jul 25 2014

STATUS

approved

URL: https://oeis.org/A245508

⇱ A245508 - OEIS