A175076 Composites c which end at 2 under iterations of {r mod (max prime p < r)} starting at r = c.

9, 15, 21, 25, 28, 33, 36, 39, 45, 49, 52, 55, 58, 63, 66, 69, 75, 78, 81, 85, 88, 91, 94, 96, 99, 105, 111, 115, 118, 120, 122, 126, 129, 133, 136, 141, 144, 146, 148, 153, 156, 159, 162, 165, 169, 172, 175, 178, 183, 186, 188, 190, 195, 201, 204, 206, 208, 213, 216

Offset

1,1

Comments

Subsequence of A175072. Union of a(n) and A175075 is A175072.

Links

Table of n, a(n) for n=1..59.

Example

Iteration procedure for a(2) = 15: 15 mod 13 = 2. Iteration procedure for a(5) = 28: 28 mod 23 = 5, 5 mod 3 = 2.

Mathematica

ce2Q[n_]:=NestWhileList[Mod[#, NextPrime[#, -1]]&, n, #>0&][[-2]]==2; Select[ Range[ 300], CompositeQ[#]&&ce2Q[#]&] (* Harvey P. Dale, Feb 09 2015 *)

Crossrefs

Sequence in context: A046446 A046350 A225438 * A046337 A359596 A046315

Adjacent sequences: A175073 A175074 A175075 * A175077 A175078 A175079

Keyword

nonn

Author

Jaroslav Krizek, Jan 23 2010

Extensions

More terms from R. J. Mathar, Sep 25 2010

Status

approved