A261570 -id:A261570 - cp's OEIS frontend

A261411 a(1)=1; thereafter a(n) = smallest prime factor of A261570(n).

1, 11, 3, 11, 41, 3, 239, 11, 3, 11, 11, 3, 11, 11, 3, 11, 11, 3, 71, 21557, 19, 17, 31, 181, 17, 353, 19, 31, 19, 29, 17, 29, 11616377, 214141, 19, 5471, 17, 13883, 3, 7, 421219193, 3, 17, 7, 3, 7, 101, 3, 634324033999, 13, 19, 13, 83, 13, 23, 13, 19, 13, 19

Offset: 1

N. J. A. Sloane, Aug 24 2015, based on Robert G. Wilson v's comment in A261570

nonn

			A261570(11) = 12345678911987654321 = (11)(59)(34631)(43117)(6373)(1999), so a(10) = 11.
Note that a(2007) = A261570(2007) is a 21233-digit (probable) prime.

David Broadhurst and Hiroaki Yamanouchi, Table of n, a(n) for n = 1..99 (First 61 terms from Hiroaki Yamanouchi)

Cf. A261570, A067063, A075023.

a(41)-a(59) from Hiroaki Yamanouchi, Aug 24 2015

A261138 The concatenation of 123456...n and the reverse of this number.

Original entry on oeis.org

11, 1221, 123321, 12344321, 1234554321, 123456654321, 12345677654321, 1234567887654321, 123456789987654321, 1234567891001987654321, 12345678910111101987654321, 123456789101112211101987654321, 1234567891011121331211101987654321, 12345678910111213144131211101987654321

Offset: 1

Umut Uludag, Aug 10 2015

Let R(n) denote the number obtained by formally reversing the digits of n, including any leading zeros that may appear; a(n) is the decimal concatenation of 1,2,...,n,R(n),R(n-1),...,R(3),R(2),R(1). - N. J. A. Sloane, Dec 01 2021
A palindromic version of A173426.
Has same start as A259937, but A259937 generates non-palindromic terms for n>9.
All terms are multiples of 11 (cf. A349805).

			For n=10 we concatenate 1,2,3,...,10,01,9,8,...3,2,1 getting 1234567891001987654321.

Cf. A002477, A173426, A259937, A261570, A349805.

with(StringTools);
myReverse := n -> Reverse(convert(n,string));
A349804:=proc(n) local i,L,R;
L:=""; R:="";
for i from n to 1 by -1 do
L:=Join( [convert(i,string), L],"");
R:=Join( [R, myReverse(convert(i,string))],"");
od:
parse(Join([L,R],""));
end proc; # N. J. A. Sloane, Dec 01 2021
# second Maple program:
a:= n-> (s-> parse(cat(s, seq(s[-i], i=1..length(s)))))(cat("", $1..n)):
seq(a(n), n=1..14); # Alois P. Heinz, Dec 01 2021

Table[d = Flatten[IntegerDigits /@ Range@ n]; FromDigits@ Flatten[{d, Reverse@ d}], {n, 13}] (* Michael De Vlieger, Aug 20 2015 *)

def A349804(n): return int((lambda x: x+x[::-1])(''.join(str(d) for d in range(1,n+1)))) # Chai Wah Wu, Dec 01 2021

a(n) = concatenate( A007908(n), A138793(n) retaining leading zeros).

More than the usual number of terms are shown in order to distinguish this from several similar sequences.

Edited by N. J. A. Sloane, Dec 11 2021

cp's OEIS Frontend

A261411 a(1)=1; thereafter a(n) = smallest prime factor of A261570(n).

Views

Author

Keywords

Examples

Links

Crossrefs

Extensions

A261138 The concatenation of 123456...n and the reverse of this number.

Views

Author

Keywords

Comments

Examples

Crossrefs

Programs

Maple

Mathematica

Python

Formula

Extensions