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A272550 Lexicographically earliest increasing sequence of primes such that odd indexed terms have final digit 1 and even indexed terms have final digit 9. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A049719 A155555 A152091 * A122869 A106535 A178150

Adjacent sequences:  A272547 A272548 A272549 * A272551 A272552 A272553

KEYWORD

nonn,easy,base

AUTHOR

Giovanni Teofilatto, May 11 2016

STATUS

approved

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Last modified June 19 00:55 EDT 2019. Contains 324217 sequences. (Running on oeis4.)