A068704 -id:A068704 - cp's OEIS frontend

A090558 Duplicate of A068704.

11, 421, 31, 41, 2551, 61, 71, 6481, 8191, 101

Offset: 1

dead

A242645 a(n) = concatenation of decimal expansions of powers of 11 (in decreasing order).

1, 111, 121111, 1331121111, 146411331121111, 161051146411331121111, 1771561161051146411331121111, 194871711771561161051146411331121111, 214358881194871711771561161051146411331121111, 2357947691214358881194871711771561161051146411331121111

Offset: 0

N. J. A. Sloane, May 23 2014

A068704(11) (presently unknown) is either 0, if every term here is composite, or the index of the first prime in the sequence.

Alois P. Heinz, Table of n, a(n) for n = 0..42

Cf. A068704, A242646.

a:= proc(n) option remember;
      `if`(n=0, 1, parse(cat(11^n, a(n-1))))
    end:
seq(a(n), n=0..10);  # Alois P. Heinz, May 24 2014

a(n) is the concatenation of 11^n, 11^(n-1), ..., 121, 11, 1.

A267720 The smallest prime number formed by the concatenation of consecutive powers of n beginning with 1^0 = "1," and ending with a trailing "1" - or "0," if no such prime number exists.

Original entry on oeis.org

0, 131, 1416641, 151, 16361, 17491, 181, 191, 0, 1111211, 11214417282073624883229859841, 0, 11419627441, 1151, 1162564096655361048576167772162684354564294967296687194767361099511627776175921860444161, 1171, 1181, 11936168591, 1201

Offset: 2

Thomas S. Pedigo, Jan 19 2016

It is not known whether solutions exist for A(2), A(10), or A(13); if there are any, they must be greater than 10^128.
A(10) has final exponent 35; "110100100010000...1000000000000000000000000000000000001", total length 667 digits. - Dana Jacobsen, Jan 22 2016
A(2) has exponent > 1100, length > 182841 digits.  A(13) has exponent > 750, length > 314093 digits. - Dana Jacobsen, Jan 25 2016

			A(14)=11419627441; 14^0=1; 14^1=14; 14^2=196; 14^3=2744; 11419627441 is prime.
A(19)=11936168591; 19^0=1; 19^1=19; 19^2=361; 19^3=6859; 11936168591 is prime.

Cf. A068704, A088622.

lim = 60; Table[SelectFirst[Rest@ FoldList[FromDigits@ Join[Most@ IntegerDigits@ #1, IntegerDigits[n^#2], {1}] &, 11, Range@ lim], PrimeQ], {n, 2, 20}] /. k_ /; MissingQ@ k -> 0 (* Michael De Vlieger, Jan 25 2016, Version 10.2 *)

a(8) corrected by Thomas S. Pedigo, Dec 08 2021

cp's OEIS Frontend

A090558 Duplicate of A068704.

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A242645 a(n) = concatenation of decimal expansions of powers of 11 (in decreasing order).

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A267720 The smallest prime number formed by the concatenation of consecutive powers of n beginning with 1^0 = "1," and ending with a trailing "1" - or "0," if no such prime number exists.

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