A280643 -id:A280643 - cp's OEIS frontend

A280642 Numbers k such that k^3 has an odd number of digits and the middle digit is 2.

5, 9, 103, 113, 133, 146, 151, 154, 165, 180, 198, 202, 470, 473, 493, 496, 504, 507, 521, 531, 538, 542, 566, 569, 581, 591, 593, 599, 612, 618, 620, 650, 654, 673, 681, 686, 703, 711, 715, 728, 729, 732, 740, 779, 801, 829, 841, 850, 855, 856, 857, 858, 874

Offset: 1

Lars Blomberg, Jan 07 2017

The sequence of cubes starts: 125, 729, 1092727, 1442897, 2352637, 3112136, 3442951, 3652264, ...

			5^3 = 1(2)5, 180^3 = 583(2)000, 618^3 = 2360(2)9032.

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-A280641, A280643-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[0,874],OddQ[Length[IntegerDigits[#^3]]] && a[#^3]==2 &] (* Indranil Ghosh, Mar 06 2017 *)

isok(k) = my(d=digits(k^3)); (#d%2 == 1) && (d[#d\2 +1] == 2);
for(k=0, 874, if(isok(k)==1, print1(k, ", "))); \\ Indranil Ghosh, Mar 06 2017

i=0
j=1
while i<=874:
    n=str(i**3)
    l=len(n)
    if l%2 and n[(l-1)//2]=="2":
        print(str(i), end=', ')
        j+=1
    i+=1 # Indranil Ghosh, Mar 06 2017

A280644 Numbers k such that k^3 has an odd number of digits and the middle digit is 4.

Original entry on oeis.org

7, 104, 112, 140, 143, 158, 166, 186, 188, 195, 465, 467, 490, 541, 558, 572, 595, 598, 604, 605, 606, 607, 613, 616, 622, 625, 630, 634, 635, 640, 643, 647, 653, 667, 675, 679, 687, 702, 712, 718, 720, 727, 734, 738, 759, 764, 783, 787, 802, 810, 815, 818

Offset: 1

Lars Blomberg, Jan 07 2017

The sequence of cubes starts: 343, 1124864, 1404928, 2744000, 2924207, 3944312, 4574296, 6434856, ...

			7^3 = 3(4)3, 195^3 = 741(4)875, 640^3 = 2621(4)4000

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-A280643, A280645-A280649, A181354.
See A279420-A279429 for a k^2 version.
See A279430-A279431 for a k^2 version in base 2.

Select[Range[1000],OddQ[IntegerLength[#^3]]&&NumberDigit[#^3,(IntegerLength[ #^3]-1)/2]==4&] (* Harvey P. Dale, Aug 12 2021 *)

cp's OEIS Frontend

A280642 Numbers k such that k^3 has an odd number of digits and the middle digit is 2.

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