

A088629


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


3



1, 3, 7, 19, 9, 13, 27, 11, 29, 21, 17, 23, 61, 33, 31, 37, 41, 47, 49, 39, 43, 51, 57, 59, 79, 63, 53, 87, 69, 67, 81, 71, 73, 91, 83, 77, 93, 89, 103, 99, 113, 97, 117, 101, 119, 133, 111, 109, 121, 123, 131, 127, 129, 139, 147, 149, 107, 151, 141, 161, 153, 137, 179
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OFFSET

1,2


COMMENTS

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


LINKS



EXAMPLE

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.


PROG

(Python)
from sympy import isprime
from itertools import count, islice
def agen():
aset, mink = set(), 1
for n in count(1):
s, k = str(n), mink
while k in aset or not isprime(int(s + str(k))): k += 1
while mink%5 == 0 or mink in aset: mink += 2
yield k; aset.add(k)


CROSSREFS



KEYWORD

base,nonn


AUTHOR



EXTENSIONS



STATUS

approved



