A362117 Concatenation of first n numbers in base 5.

1, 12, 123, 1234, 123410, 12341011, 1234101112, 123410111213, 12341011121314, 1234101112131420, 123410111213142021, 12341011121314202122, 1234101112131420212223, 123410111213142021222324, 12341011121314202122232430, 1234101112131420212223243031

Offset: 1

Author

Michael S. Branicky and N. J. A. Sloane, Apr 19 2023

Keywords

• nonn
• base

Comments

When regarded as decimal numbers, the first prime in this sequence is a(6) = 12341011.

a(8) is also prime and for n <= 2000, a(n) is not prime except for n = 6 or 8. - Chai Wah Wu, Apr 19 2023

Crossrefs

Cf. A362118, A058935, A360502, A117640, A007908.

Programs

Mathematica

A362117[n_]:=FromDigits[Flatten[IntegerDigits[Range[n],5]]];Array[A362117,20] (* Paolo Xausa, Nov 27 2023 *)

Python

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