A272550 Lexicographically earliest increasing sequence of primes such that odd-indexed terms have final digit 1 and even-indexed terms have final digit 9.

11, 19, 31, 59, 61, 79, 101, 109, 131, 139, 151, 179, 181, 199, 211, 229, 241, 269, 271, 349, 401, 409, 421, 439, 461, 479, 491, 499, 521, 569, 571, 599, 601, 619, 631, 659, 661, 709, 751, 769, 811, 829, 881, 919, 941, 1009, 1021, 1039, 1051, 1069, 1091, 1109

Offset

1,1

Comments

a(n) + a(n+1) = 0 (mod 10) for all n >= 1.

Links

Alois P. Heinz, Table of n, a(n) for n = 1..10000

Maple

a:= proc(n) option remember; local p, d;
      if n=1 then p:= 11
    else p:= a(n-1); d:= `if`(n::odd, 1, 9);
         while irem(p, 10)<>d do p:=nextprime(p) od
      fi; p
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, May 11 2016

Mathematica

a[1] = 11; a[n_] := a[n] = Block[{d, q = a[n-1]}, d=10-Mod[q, 10]; While[ Mod[q = NextPrime@ q, 10] != d]; q]; Array[a, 30] (* Giovanni Resta, May 11 2016 *)

Crossrefs

Sequence in context: A155555 A357426 A152091 * A122869 A106535 A178150

Adjacent sequences: A272547 A272548 A272549 * A272551 A272552 A272553

Keyword

nonn,easy,base

Author

Giovanni Teofilatto, May 11 2016

Status

approved