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A090513 Least m exceeding the previous term such that the concatenation mnm is prime. 2
3, 7, 11, 17, 21, 23, 111, 121, 137, 183, 1003, 1031, 1047, 1081, 1103, 1131, 1153, 1249, 1253, 1273, 1277, 1301, 1317, 1321, 1323, 1333, 1343, 1371, 1387, 1439, 1463, 1467, 1469, 1473, 1549, 1589, 1617, 1621, 1727, 1763, 1779, 1787, 1791, 1867, 1883, 1901 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..231
EXAMPLE
313, 727, 11311, etc. are primes.
MATHEMATICA
nxt[{a_, b_}]:=Module[{m=b+2, idn=IntegerDigits[a+1]}, While[!PrimeQ[ FromDigits[ Join[IntegerDigits[m], idn, IntegerDigits[m]]]], m=m+2]; {a+1, m}]; Transpose[NestList[nxt, {1, 3}, 40]][[2]] (* Harvey P. Dale, Sep 26 2012 *)
PROG
(Python)
from sympy import isprime
from itertools import count, islice
def agen(): # generator of terms
m = 1
for n in count(1):
while not isprime(int(str(m)+str(n)+str(m))):
m += 2
yield m
m += 2
print(list(islice(agen(), 46))) # Michael S. Branicky, Aug 10 2022
CROSSREFS
Sequence in context: A119992 A023249 A249682 * A285600 A191050 A081515
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Dec 06 2003
EXTENSIONS
More terms from Ray G. Opao, Nov 18 2004
a(36) and beyond from Michael S. Branicky, Aug 09 2022
STATUS
approved

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Last modified June 22 01:41 EDT 2024. Contains 373561 sequences. (Running on oeis4.)