A216309 The prime ending in 1 is the only prime in a decade.

181, 211, 241, 421, 631, 661, 691, 811, 1021, 1051, 1171, 1201, 1381, 1471, 1511, 1531, 1801, 1811, 1831, 1951, 2161, 2221, 2251, 2311, 2521, 2621, 2731, 2861, 2971, 3001, 3121, 3191, 3271, 3331, 3361, 3391, 3571, 3931, 4111, 4201, 4231, 4261, 4621, 4691

Offset: 1

Author

V. Raman, Sep 03 2012

Keywords

• nonn
• base
• easy

Comments

Primes of the form 10n+1 such that 10n+3, 10n+7, and 10n+9 are composite. - Charles R Greathouse IV, Sep 06 2012

Links

• V. Raman, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A030430. Cf. A032352, A007811, A078494.

Programs

Mathematica

t = {}; Do[ps = Select[Range[10*n, 10*n + 9], PrimeQ]; If[ps == {10*n + 1}, AppendTo[t, ps[[1]]]], {n, 0, 588}]; t (* T. D. Noe, Sep 04 2012 *)
Select[10*Range[500]+1,PrimeQ[#]&&AllTrue[#+{2,6,8},CompositeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Dec 01 2018 *)

Formula

a(n) ~ 4n log n. - Charles R Greathouse IV, Sep 06 2012