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A088629 Smallest number k not included earlier such that the concatenation n, k is a prime. 3

%I #12 Aug 20 2022 13:37:47

%S 1,3,7,19,9,13,27,11,29,21,17,23,61,33,31,37,41,47,49,39,43,51,57,59,

%T 79,63,53,87,69,67,81,71,73,91,83,77,93,89,103,99,113,97,117,101,119,

%U 133,111,109,121,123,131,127,129,139,147,149,107,151,141,161,153,137,179

%N Smallest number k not included earlier such that the concatenation n, k is a prime.

%C Another rearrangement of odd numbers not == 0 (mod 5).

%H Michael S. Branicky, <a href="/A088629/b088629.txt">Table of n, a(n) for n = 1..10000</a>

%e a(4) = 19. Though 41, 43 and 47 are prime 1, 3 and 7 have been included earlier and also 49, 411, 413 and 417 are not prime hence 419 is the required prime.

%o (Python)

%o from sympy import isprime

%o from itertools import count, islice

%o def agen():

%o aset, mink = set(), 1

%o for n in count(1):

%o s, k = str(n), mink

%o while k in aset or not isprime(int(s + str(k))): k += 1

%o while mink%5 == 0 or mink in aset: mink += 2

%o yield k; aset.add(k)

%o print(list(islice(agen(), 63))) # _Michael S. Branicky_, Aug 20 2022

%Y Cf. A045572, A088630.

%K base,nonn

%O 1,2

%A _Amarnath Murthy_, Oct 21 2003

%E More terms from _Ray G. Opao_, Aug 19 2004

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Last modified May 24 06:10 EDT 2024. Contains 372772 sequences. (Running on oeis4.)