A221309 Numbers m such that no subset of {m-1, m, m+1} sums up to a prime number.

25, 77, 85, 92, 93, 94, 118, 122, 123, 124, 133, 143, 144, 145, 160, 161, 170, 171, 185, 188, 202, 203, 206, 207, 208, 213, 214, 218, 235, 236, 237, 247, 248, 253, 259, 265, 266, 267, 275, 287, 290, 291, 295, 298, 302, 305, 319, 325, 328, 333, 334, 335, 340

Offset

1,1

Comments

A117499(a(n)) = 0.

Links

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

Example

a(1) = 25: there are 7 nonempty subsets of {25-1, 25, 25+1}: {24}, {25}, {26}, {24,25}, {24,26}, {25,26} and {24,25,26} with sums and factorizations: 24=3*2^3, 25=5^2, 26=13*2, 49=7^2, 50=5^2*2, 51=17*3 and 75=5^2*3.

Mathematica

Flatten@Position[
  Plus @@ # & /@ (Rest@Subsets[# + {-1, 0, 1}]) & /@
Range@340, {_?(! PrimeQ@# &) ..}] (* Hans Rudolf Widmer, Oct 26 2024 *)

Prog

(Haskell)
a221309 n = a221309_list !! (n-1)
a221309_list = map (+ 1) $ elemIndices 0 a117499_list

Crossrefs

Subsequence of A079364.

Sequence in context: A042228 A042230 A189642 * A192504 A363635 A033658

Adjacent sequences: A221306 A221307 A221308 * A221310 A221311 A221312

Keyword

nonn

Author

Reinhard Zumkeller, Jan 10 2013

Status

approved