cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-6 of 6 results.

A102139 Iccanobirt prime indices (9 of 15): Indices of prime numbers in A102119.

Original entry on oeis.org

4, 6, 7, 11, 15, 19, 233, 549, 1608, 4143, 4633, 9642
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Comments

No more terms through 5000.
a(13) > 50000. - Robert Price, Nov 09 2018

Crossrefs

Programs

  • Mathematica
    a[n_] := a[n] =
       IntegerReverse[(a[n - 1] + a[n - 2] + IntegerReverse[a[n - 3]])];
    a[0] = 0; a[1] = 0; a[2] = 1;
    Select[Range[0, 5000], PrimeQ[a[#]] &] (* Robert Price, Apr 10 2020 *)

Formula

A102119(a(n)) = A102159(n).

Extensions

a(12) from Robert Price, Nov 09 2018

A102159 Iccanobirt primes (9 of 15): Prime numbers in A102119.

Original entry on oeis.org

2, 7, 31, 401, 90481, 6691411
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Comments

Next term is too large to include.

Crossrefs

Formula

a(n) = A102119(A102139(n)).

Extensions

Offset changed to 1 by Jinyuan Wang, Aug 14 2021

A102179 Iccanobirt semiprime indices (9 of 15): Indices of semiprime numbers in A102119.

Original entry on oeis.org

5, 9, 17, 18, 20, 25, 28, 29, 35, 41, 48, 50, 51, 58, 67, 74, 90, 94, 107, 108, 135, 137, 159, 165, 186, 254, 290
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Crossrefs

Formula

A102119(a(n)) = A102199(n).

Extensions

Offset changed to 1 and a(26)-a(27) from Jinyuan Wang, Aug 14 2021

A102199 Iccanobirt semiprimes (9 of 15): Semiprime numbers in A102119.

Original entry on oeis.org

4, 26, 122309, 918349, 1892158, 46917727, 25411507, 629951893, 444564787601, 47147317432111, 6249165484647581, 68535341599076501, 49254291193918837, 70468687493735802121, 806424054403260562011601, 1987232535137485809825804281, 7450185554509682737733199157763041
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Crossrefs

Formula

a(n) = A102119(A102179(n)).

Extensions

Offset changed to 1 and more terms from Jinyuan Wang, Aug 14 2021

A102111 Iccanobirt numbers (1 of 15): a(n) = a(n-1) + a(n-2) + R(a(n-3)), where R is the digit reversal function A004086.

Original entry on oeis.org

0, 0, 1, 1, 2, 4, 7, 13, 24, 44, 99, 185, 328, 612, 1521, 2956, 4693, 8900, 20185, 33049, 53332, 144483, 291848, 459666, 1135955, 2443813, 4246722, 12285846, 19716010, 34278280, 118852511, 154192582, 281332336, 550783729, 1117407516, 2301424427
Offset: 0

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 30 2004

Keywords

Comments

Digit reversal variation of tribonacci numbers A000073.
Inspired by Iccanobif numbers: A001129, A014258-A014260.

Crossrefs

Programs

  • Magma
    a:=[0,0,1];[n le 3 select a[n] else Self(n-1) + Self(n-2) + Seqint(Reverse(Intseq(Self(n-3)))):n in [1..36]]; // Marius A. Burtea, Oct 23 2019
  • Maple
    read("transforms") ;
    A102111 := proc(n)
        option remember;
        if n <= 2 then
            return op(n+1,[0,0,1]) ;
        else
            return procname(n-1)+procname(n-2)+digrev(procname(n-3)) ;
        end if;
    end proc:
    seq(A102111(n),n=0..20) ; # R. J. Mathar, Nov 17 2012
  • Mathematica
    R[n_]:=FromDigits[Reverse[IntegerDigits[n]]];Clear[a];a[0]=0;a[1]=0;a[2]=1;a [n_]:=a[n]=a[n-1]+a[n-2]+R[a[n-3]];Table[a[n], {n, 0, 40}]
    nxt[{a_,b_,c_}]:={b,c,IntegerReverse[a]+b+c}; NestList[nxt,{0,0,1},40][[;;,1]] (* Harvey P. Dale, Jul 18 2023 *)
  • Python
    def R(n):
      n_str = str(n)
      reversedn_str = n_str[::-1]
      reversedn = int(reversedn_str)
      return reversedn
    def A(n):
      if n == 0:
        return 0
      elif n == 1:
        return 0
      elif n == 2:
        return 1
      elif n >= 3:
        return A(n-1)+A(n-2)+R(A(n-3))
    for i in range(0,20):
      print(A(i)) # Dylan Delgado, Oct 23 2019
    

Formula

A004086(a(n)) = A102119(n).

A102118 Iccanobirt numbers (8 of 15): a(n) = R(a(n-1) + a(n-2) + a(n-3)), where R is the digit reversal function A004086.

Original entry on oeis.org

0, 0, 1, 1, 2, 4, 7, 31, 24, 26, 18, 86, 31, 531, 846, 8041, 8149, 63071, 16297, 71578, 649051, 629637, 6620531, 9129987, 55108361, 97885807, 551421261, 924514407, 5741283751, 9149127127, 58252941851, 92725334137, 511304721061
Offset: 0

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 30 2004

Keywords

Comments

Digit reversal variation of tribonacci numbers A000073.
Inspired by Iccanobif numbers: A001129, A014258-A014260.

Crossrefs

Programs

  • Mathematica
    R[n_]:=FromDigits[Reverse[IntegerDigits[n]]];Clear[a];a[0]=0;a[1]=0;a[2]=1;a [n_]:=a[n]=R[a[n-1]+a[n-2]+a[n-3]];Table[a[n], {n, 0, 40}]
    Transpose[NestList[{#[[2]],#[[3]],FromDigits[Reverse[IntegerDigits[Total[ #]]]]}&,{0,0,1},40]][[1]] (* Harvey P. Dale, Dec 04 2012 *)

Extensions

Incorrect formula removed by Georg Fischer, Dec 18 2020
Showing 1-6 of 6 results.