A280642 -id:A280642 - cp's OEIS frontend

A280641 Numbers k such that k^3 has an odd number of digits and the middle digit is 1.

1, 6, 8, 23, 44, 45, 102, 106, 110, 114, 117, 121, 137, 148, 152, 153, 162, 168, 176, 185, 189, 194, 206, 210, 478, 488, 512, 533, 553, 560, 574, 580, 626, 639, 655, 662, 669, 671, 676, 682, 683, 684, 685, 693, 704, 710, 730, 731, 737, 742, 758, 761, 767, 771

Offset: 1

Lars Blomberg, Jan 07 2017

The sequence of cubes starts: 1, 216, 512, 12167, 85184, 91125, 1061208, 1191016, ...

			1^3 = (1), 114^3 = 148(1)544, 560^3 = 1756(1)6000

Lars Blomberg, Table of n, a(n) for n = 1..10000
Jeremy Gardiner, Middle digit in cube numbers, Seqfan Mailing list, Dec 12 2016.

Cf. A280640, A280642-A280649, A181354.
See A279420-A279429 for a k^2 version.
See A279430-A279431 for a k^2 version in base 2.

a[n_]:=Part[IntegerDigits[n], (Length[IntegerDigits[n]] + 1)/2];
Select[Range[0, 771], OddQ[Length[IntegerDigits[#^3]]] && a[#^3]==1 &] (* Indranil Ghosh, Mar 06 2017 *)

isok(k) = my(d=digits(k^3)); (#d%2 == 1) && (d[#d\2 +1] == 1);
for(k=0, 771, if(isok(k)==1, print1(k, ", "))); \\ Indranil Ghosh, Mar 06 2017

i=0
j=1
while i<=771:
    n=str(i**3)
    l=len(n)
    if l%2 and n[(l-1)//2]=="1":
        print(str(i), end=', ')
        j+=1
    i+=1 # Indranil Ghosh, Mar 06 2017

A280643 Numbers k such that k^3 has an odd number of digits and the middle digit is 3.

Original entry on oeis.org

29, 34, 39, 46, 118, 125, 141, 142, 155, 161, 170, 211, 213, 477, 489, 511, 522, 526, 529, 535, 554, 573, 582, 586, 589, 631, 632, 633, 645, 663, 680, 691, 699, 723, 733, 744, 747, 770, 785, 790, 816, 817, 832, 854, 859, 863, 869, 873, 878, 892, 897, 901, 923

Offset: 1

Lars Blomberg, Jan 07 2017

The sequence of cubes starts: 24389, 39304, 59319, 97336, 1643032, 1953125, 2803221, 2863288, ...

			29^3 = 24(3)89, 161^3 = 417(3)281, 663^3 = 2914(3)4247.

Lars Blomberg, Table of n, a(n) for n = 1..10000
Jeremy Gardiner, Middle digit in cube numbers, Seqfan Mailing list, Dec 12 2016.

Cf. A280640-A280642, A280644-A280649, A181354.
See A279420-A279429 for a k^2 version.
See A279430-A279431 for a k^2 version in base 2.

Select[Range[925],OddQ[len=Length[IntegerDigits[#^3]]]&&Part[IntegerDigits[#^3],(len+1)/2]==3 &] (* Stefano Spezia, Oct 03 2023 *)

cp's OEIS Frontend

A280641 Numbers k such that k^3 has an odd number of digits and the middle digit is 1.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

Programs

Mathematica

PARI

Python