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A066811 Numbers k such that the concatenation of odd numbers from 1 to k is a prime. 3
3, 19, 31, 67, 97, 5139 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
FORMULA
a(n) = 2*A046036(n) - 1. - Michel Marcus, Jan 31 2014
EXAMPLE
19 is a term because 135791113151719 is a prime.
MATHEMATICA
p = ""; Do[p = p <> ToString[2*n+1]; If[PrimeQ[ToExpression[p]], Print[2*n+1]], {n, 0, 2569}] (* Ryan Propper, Aug 26 2005 *)
PROG
(Python)
from sympy import isprime
def agen():
k, str1tok = 1, '1'
while True:
if isprime(int(str1tok)): yield k
k, str1tok = k + 2, str1tok + str(k + 2)
g = agen()
print([next(g) for i in range(5)]) # Michael S. Branicky, Mar 19 2021
CROSSREFS
Sequence in context: A236969 A222590 A107165 * A269414 A162307 A128069
KEYWORD
base,nonn
AUTHOR
Patrick De Geest, Jan 20 2002
EXTENSIONS
a(6) from Ryan Propper, Aug 26 2005
STATUS
approved

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Last modified March 29 02:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)