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

2,1

Links

Table of n, a(n) for n=2..79.

Formula

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

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

Example

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.

Prog

(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

Crossrefs

Cf. A020639, A098129.

Sequence in context: A151686 A201555 A348456 * A293753 A164554 A141908

Adjacent sequences: A358272 A358273 A358274 * A358276 A358277 A358278

Keyword

nonn

Author

David Cleaver, Mar 26 2023

Status

approved