A358275 Least prime factor of A098129(n).

2, 71, 2, 5, 2, 1141871, 2, 3, 2, 58728589, 2, 3, 2, 5, 2, 3, 2, 277, 2, 4643, 2, 29, 2, 5, 2, 3, 2, 37, 2, 3, 2, 13, 2, 3, 2, 264439098646852541, 2, 7, 2, 53, 2, 7, 2, 3, 2, 587, 2, 3, 2, 45307, 2, 3, 2, 5, 2, 11, 2, 7, 2, 13, 2, 3, 2, 5, 2, 3, 2, 17, 2, 3, 2, 983, 2, 5, 2, 53, 2, 11

Offset: 2

Author

David Cleaver, Mar 26 2023

Keywords

• nonn

Examples

			a(3) = 71 because 71 is the smallest prime factor of A098129(3) = 122333.
a(7) = 1141871 because 1141871 is the smallest prime factor of A098129(7) = 1223334444555556666667777777.
		

Crossrefs

Cf. A020639, A098129.

Programs

Python

from sympy import primefactors
def A358275(n): return min(primefactors(int(''.join(str(j)*j for j in range(1,n+1))))) if n&1 else 2 # Chai Wah Wu, Apr 15 2023

Formula

a(n) = A020639(A098129(n)).

a(n) = 2 if n is even. - Chai Wah Wu, Apr 15 2023