A216311 The prime ending in 7 is the only prime in a decade.

97, 127, 307, 367, 397, 457, 487, 557, 587, 727, 787, 797, 877, 907, 937, 967, 1087, 1117, 1447, 1567, 1597, 1637, 1657, 1777, 1847, 1987, 2437, 2467, 2617, 2647, 2707, 2767, 2777, 2887, 2897, 2917, 2927, 3037, 3137, 3217, 3407, 3457, 3607, 3727, 3847

Offset: 1

Author

V. Raman, Sep 03 2012

Keywords

• nonn
• base
• easy

Comments

Primes of the form 10n+7 such that 10n+1, 10n+3, 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 A030432.

Cf. A032352, A007811, A078494.

Programs

Magma

[p: p in PrimesUpTo(4000) | p mod 10 eq 7 and IsOne(#PrimesInInterval(10*t+1, 10*t+9)) where t is Floor(p/10)]; // Bruno Berselli, Sep 14 2012

Mathematica

t = {}; Do[ps = Select[Range[10*n, 10*n + 9], PrimeQ]; If[ps == {10*n + 7}, AppendTo[t, ps[[1]]]], {n, 0, 529}]; t (* T. D. Noe, Sep 04 2012 *)

Formula

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