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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 (list; graph; refs; listen; history; text; internal format)
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)
print(list(islice(agen(), 63))) # Michael S. Branicky, Aug 20 2022
CROSSREFS
Sequence in context: A361087 A212848 A217371 * A075609 A083439 A151858
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Oct 21 2003
EXTENSIONS
More terms from Ray G. Opao, Aug 19 2004
STATUS
approved

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Last modified April 14 00:20 EDT 2024. Contains 371652 sequences. (Running on oeis4.)