This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
mx = 5; t = Table[-1, {mx}]; n = 0; found = 0; While[found < mx, ps = Select[Range[10*n, 10*n + 9], PrimeQ]; len = Length[ps]; If[t[[len + 1]] == -1, t[[len + 1]] = n; found++]; n++]; t (* T. D. Noe, Sep 03 2012 *)
8 is a term because 8 - 1 = 7 and 7 is prime and 8/5 = 1.6 which when rounded gives 2 and 2 is also prime.
235 is not a term because 235 - 1 = 234 and 234 is not a prime although 235/5 = 47 is prime.
Initial terms, associated primes and d:
k k - 1 round(k/5) d
a(1) 8 7 2
a(2) 12 11 2 0
a(3) 14 13 3 1
a(4) 24 23 5 2
a(5) 54 53 11 6
a(6) 84 83 17 6
a(7) 114 113 23 6
a(8) 234 233 47 24
a(9) 264 263 53 6
a(10) 294 293 59 6
Select[Range[2,5000,2],And@@PrimeQ[{#-1,Round[#/5]}]&] (* Giorgos Kalogeropoulos, Apr 01 2021 *)
for(k = 1,10000,if(isprime(k - 1) && isprime(k\/5),print1(k", ")))
from sympy import isprime A342809_list = [k for k in range(1,10**5) if isprime(k-1) and isprime(k//5+int(k % 5 > 2))] # Chai Wah Wu, Apr 08 2021
a(1) = 100630 since 1006301, 1006303, 1006307, 1006309, 1006331, 1006333, 1006337, and 1006339 are all prime and there are no smaller minimally close prime decades.
from itertools import count
from sympy import isprime
def generate_a() :
for k in count() :
for j in (1,3,7,9,31,33,37,39) :
if not isprime(10*k+j) : break
else:
yield k
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