A175208 a(1) = 1, a(2) = 7, for n >= 3, a(n) = smallest prime > a(n-1) such that a(n) mod a(n-1) = a(n-2).

1, 7, 29, 181, 4373, 61403, 2583299, 41394187, 85371673, 895110917, 16197368179, 98079319991, 800831928107, 3301407032419, 159268369484219, 5736962708464303, 46054970037198643, 4703343906502725889, 18859430596048102199, 155578788674887543481, 4375065513492899319667

Offset

1,2

Comments

It appears that the definition should include the condition that the sequence is strictly increasing - true? - N. J. A. Sloane, Jan 27 2019

a(390) has 1002 digits. - Michael S. Branicky, Dec 21 2023

Links

Michael S. Branicky, Table of n, a(n) for n = 1..389 (terms 1..33 from Charlie Neder)

Prog

(Python)
from gmpy2 import is_prime
from itertools import count, islice
def agen(): # generator of terms
    c, b = 1, 7
    yield from [c, b]
    for n in count(3):
        a = next(c + b*i for i in count(1) if is_prime(c+b*i))
        c, b = b, a
        yield a
print(list(islice(agen(), 21))) # Michael S. Branicky, Dec 21 2023

Crossrefs

Cf. A175093, A175094, A175207.

Sequence in context: A297677 A287860 A347814 * A307954 A071918 A183434

Adjacent sequences: A175205 A175206 A175207 * A175209 A175210 A175211

Keyword

nonn

Author

Jaroslav Krizek, Mar 04 2010

Extensions

a(12)-a(20) from Charlie Neder, Jan 25 2019

Name corrected per N. J. A. Sloane's comment by Michael S. Branicky, Dec 21 2023

Status

approved