A175090 - OEIS

A175090

Composites c with result 0 under iterations of {r mod (max prime p <= r)} starting at r = c.

9, 10, 15, 16, 21, 22, 25, 26, 28, 33, 34, 36, 39, 40, 45, 46, 49, 50, 52, 55, 56, 58, 63, 64, 66, 69, 70, 75, 76, 78, 81, 82, 85, 86, 88, 91, 92, 94, 96, 99, 100, 105, 106, 111, 112, 115, 116, 118, 120, 122, 123, 124, 126, 129, 130, 133, 134, 136, 141, 142

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OFFSET

1,1

COMMENTS

Intersection of A002808 and A175089.

Composites c such that A121559(c) = 0. - Michel Marcus, Aug 22 2014

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

Iteration procedure for a(3) = 15: 15 mod 13 = 2, 2 mod 2 = 0.

MAPLE

g:= proc(x) if isprime(x) then 0 else x mod prevprime(x) fi end proc:

f:= proc(x) local y; y:= x; while y > 1 do y:= g(y) od; y = 0 end proc:

select(not(isprime) and f, [$4..200]); # Robert Israel, Feb 09 2015

MATHEMATICA

Composites := Select[Range[2, 200], ! PrimeQ[#] &]; Select[Composites, PrimeQ[# - NextPrime[#, -1]] &] (* Carlos Eduardo Olivieri, Feb 09 2015 *)

CROSSREFS

Cf. A007917 and A064722 (both for the iterations).

Sequence in context: A114844 A194593 A005381 * A365166 A197113 A099616

Adjacent sequences: A175087 A175088 A175089 * A175091 A175092 A175093

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Jan 28 2010

EXTENSIONS

Missing term 55 inserted, more terms added, Michel Marcus, Aug 22 2014

STATUS

approved