A308899 a(n) = largest prime factor of the number with decimal expansion 20305070...0p_n where p_n = n-th prime.

2, 29, 131, 33287, 17627, 1754975809, 59218567, 318879703697, 2030507011013017019023, 14400758943354730631369, 1016015647, 32002443156997, 2464082401591041689, 4916481866859605372937116297910511, 2030507011013017019023029031037041043047

Offset

1,1

Comments

The Honaker-Caldwell link gives a(25) =

20305070110130170190230290310370410430470530590

\61067071073079083089097,

with 70 digits.

Links

Daniel Suteu, Table of n, a(n) for n = 1..43

G. L. Honaker, Jr. and Chris Caldwell, Prime Curios!, 2030507...[70 digits]...89097.

Example

Here are Maple's factorizations of 2, 203, 20305, ... (the factors appear in random order):
2 = (2)
203 = (7)  (29)
20305 = (5)  (31)  (131)
2030507 = (61)  (33287)
2030507011 = (13)  (17627)  (8861)
2030507011013 = (13)  (89)  (1754975809)
2030507011013017 = (59218567)  (34288351)
2030507011013017019 = (7)  (547)  (1663)  (318879703697)

Mathematica

Table[FactorInteger[FromDigits[Flatten[IntegerDigits/@Riffle[Prime[Range[n]], 0]]]][[-1, 1]], {n, 20}] (* Harvey P. Dale, May 09 2021 *)

Prog

(PARI) pp = 0; forprime (p=2, 47, print1 (vecmax(factor(pp = pp * 10^(1+#digits(p)) + p)[, 1]~) ", ")) \\ Rémy Sigrist, Jul 13 2019

Crossrefs

Inspired by the comment in Bernard Schott's A309101.

Sequence in context: A123004 A062618 A128842 * A028883 A024200 A137625

Adjacent sequences: A308896 A308897 A308898 * A308900 A308901 A308902

Keyword

nonn,base

Author

N. J. A. Sloane, Jul 13 2019

Extensions

More terms from Rémy Sigrist, Jul 13 2019

Status

approved