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A249053 Defined by (i) a(1)=1; (ii) if you move a(n) steps to the right you must reach a prime; (iii) a(n) = smallest unused composite number greater than a(n-1), unless a(n) is required to be prime by (ii), in which case a(n) is the smallest unused prime greater than a(n-1). 2
1, 2, 4, 5, 6, 8, 11, 12, 13, 14, 17, 18, 20, 23, 24, 25, 26, 29, 30, 31, 32, 37, 38, 41, 42, 44, 45, 47, 48, 53, 54, 55, 59, 60, 62, 63, 67, 68, 71, 72, 73, 74, 79, 80, 81, 82, 83, 84, 89, 90, 97, 98, 101, 102, 104, 105, 106, 108, 109, 110, 113, 114, 115 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

REFERENCES

Eric Angelini, Posting to Sequence Fans Mailing List, Mar 17 2008 (the definition was clarified by Gabriel Cunningham).

LINKS

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

PROG

(Haskell)

import Data.Map (singleton, findMin, delete, insert)

a249053 n = a249053_list !! (n-1)

a249053_list = 1 : f 1 1 a002808_list (singleton 1 1) where

   f x z cs m

     | k == x    = p : f (x + 1) p cs (insert (x + p) 0 $ delete x m)

     | otherwise = c : f (x + 1) c cs' (insert (x + c) 0 m)

     where p = a007918 z

           (c:cs') = dropWhile (<= z) cs

           (k, _) = findMin m

-- Reinhard Zumkeller, Nov 01 2014

CROSSREFS

See A249054 for another version.

Cf. A002808, A007918.

Sequence in context: A093080 A059916 A099747 * A082851 A091207 A284525

Adjacent sequences:  A249050 A249051 A249052 * A249054 A249055 A249056

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Nov 01 2014

STATUS

approved

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Last modified June 26 16:18 EDT 2022. Contains 354885 sequences. (Running on oeis4.)