A362117
Concatenation of first n numbers in base 5.
Original entry on oeis.org
1, 12, 123, 1234, 123410, 12341011, 1234101112, 123410111213, 12341011121314, 1234101112131420, 123410111213142021, 12341011121314202122, 1234101112131420212223, 123410111213142021222324, 12341011121314202122232430, 1234101112131420212223243031
Offset: 1
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A362117[n_]:=FromDigits[Flatten[IntegerDigits[Range[n],5]]];Array[A362117,20] (* Paolo Xausa, Nov 27 2023 *)
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from gmpy2 import digits
def A362117(n): return int(''.join(digits(n,5) for n in range(1,n+1))) # Chai Wah Wu, Apr 19 2023
A362119
Concatenate the base-6 strings for 1,2,...,n.
Original entry on oeis.org
1, 12, 123, 1234, 12345, 1234510, 123451011, 12345101112, 1234510111213, 123451011121314, 12345101112131415, 1234510111213141520, 123451011121314152021, 12345101112131415202122, 1234510111213141520212223, 123451011121314152021222324, 12345101112131415202122232425
Offset: 1
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A362119[n_]:=FromDigits[Flatten[IntegerDigits[Range[n],6]]];Array[A362119,20] (* Paolo Xausa, Nov 27 2023 *)
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from sympy.ntheory import digits
from itertools import count, islice
def agen(s="", base=6): yield from (int(s:=s+"".join(map(str, digits(n, base)[1:]))) for n in count(1))
print(list(islice(agen(), 20)))
A362429
Smallest k such that the concatenation of the numbers 123...k in base n is prime when interpreted as a decimal number, or -1 if no such prime exists.
Original entry on oeis.org
-1, 231, 7315, 3241, 6, 12891, 22, 227, 127
Offset: 1
a(5) is 6: 12341011 (concatenate 1 though 6 in base 5) is a prime when interpreted as a decimal number.
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from gmpy2 import is_prime
from sympy.ntheory import digits
from itertools import count, islice
def c(base, s=""):
if base == 1: yield from (s:=s+"1"*n for n in count(1))
else:
yield from (s:=s+"".join(map(str, digits(n, base)[1:])) for n in count(1))
def a(n):
if n == 1: return -1
return next(k for k, t in enumerate(c(n), 1) if is_prime(int(t)))
Showing 1-3 of 3 results.
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