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

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

Offset

1,2

Comments

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

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000

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

Cf. A045572, A088630.

Sequence in context: A361087 A212848 A217371 * A075609 A083439 A151858

Adjacent sequences: A088626 A088627 A088628 * A088630 A088631 A088632

Keyword

base,nonn

Author

Amarnath Murthy, Oct 21 2003

Extensions

More terms from Ray G. Opao, Aug 19 2004

Status

approved