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

Author

N. J. A. Sloane, Jul 13 2019

Keywords

• nonn
• base

Comments

The Honaker-Caldwell link gives a(25) =

20305070110130170190230290310370410430470530590

\61067071073079083089097,

with 70 digits.

Examples

			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)
		

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.

Crossrefs

Inspired by the comment in Bernard Schott's A309101.

Programs

Mathematica

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

PARI

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

Extensions

More terms from Rémy Sigrist, Jul 13 2019