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.

A102137 Iccanobirt prime indices (7 of 15): Indices of prime numbers in A102117.

Original entry on oeis.org

4, 6, 7, 19, 43, 48, 109, 122, 628, 1689, 6208, 6309, 15479, 21651
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Comments

a(15) > 50000. - Robert Price, Nov 09 2018

Crossrefs

Cf. A000040, A102117, A102131-A102145.

Programs

  • Maple
    rev:= proc(n) local i, L;
L:= convert(n,base, 10);
add(L[-i]*10^(i-1),i=1..nops(L))
end proc:
A[0]:= 0: A[1]:= 0: A[2]:= 1:
RA[0]:=0: RA[1]:= 0: RA[2]:= 1:
count:= 0:
for n from 3 to 10000 do
  A[n]:= RA[n-1]+RA[n-2]+RA[n-3];
  RA[n]:= rev(A[n]);
  if isprime(A[n]) then count:= count+1; a[count]:= n fi
od:
seq(a[i],i=1..count); # Robert Israel, Aug 04 2016
  • Mathematica
    Flatten[Position[Transpose[NestList[nxt,{0,0,1},1700]][[1]],?PrimeQ]]-1 (* _Harvey P. Dale, Nov 28 2015 *)

Formula

A102117(a(n)) = A102157(n).

Extensions

a(11)-a(13) from Robert Israel, Aug 04 2016
a(14) from Robert Price, Nov 09 2018

A102157 Iccanobirt primes (7 of 15): Prime numbers in A102117.

Original entry on oeis.org

2, 7, 13, 87517, 2891668030768721, 70625274624238913, 103865292721379353050549556815505213549, 8541928234907492663056090579782886424256601
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Comments

Next term is too large to include.
The next term has 231 digits. - Harvey P. Dale, Dec 16 2021

Crossrefs

Cf. A000040, A102117, A102151-A102165.

Programs

  • Mathematica
    nxt[{a_,b_,c_}]:={b,c,Total[IntegerReverse/@{a,b,c}]};Select[NestList[nxt,{0,0,1},200][[All,1]],PrimeQ] (* Harvey P. Dale, Dec 16 2021 *)

Formula

a(n) = A102117(A102137(n)).

Extensions

Offset changed to 1 by Jinyuan Wang, Aug 12 2021

A102177 Iccanobirt semiprime indices (7 of 15): Indices of semiprime numbers in A102117.

Original entry on oeis.org

5, 9, 22, 29, 33, 38, 41, 54, 60, 71, 82, 100, 107, 175, 180, 193, 217, 258, 259, 282, 295, 360, 382
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Crossrefs

Cf. A001358, A102117, A102171-A102185, A102197.

Programs

Formula

A102117(a(n)) = A102197(n).

Extensions

a(17) from Robert Price, Nov 09 2018
Offset changed to 1 and a(18)-a(23) from Jinyuan Wang, Aug 12 2021

A102197 Iccanobirt semiprimes (7 of 15): Semiprime numbers in A102117.

Original entry on oeis.org

4, 62, 1350266, 7217219419, 662282997049, 131048548574311, 1476501837943501, 77398992743877949, 1009160086034826303, 7334718374224277375323, 267139368935075847112946291, 149235809291913788071835702010683, 1385662433217897970940689446154295119
Offset: 1

Views

Author

Jonathan Vos Post and Ray Chandler, Dec 31 2004

Keywords

Crossrefs

Cf. A001358, A102117, A102191-A102205.

Formula

a(n) = A102117(A102177(n)).

Extensions

Offset changed to 1 and a(13) from Jinyuan Wang, Aug 12 2021

A102125 Iccanobirt numbers (15 of 15): a(n) = R(R(a(n-1)) + R(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, 31, 42, 44, 18, 941, 472, 405, 729, 5071, 6313, 8675, 90601, 31591, 9853, 11733, 31865, 31149, 736481, 365533, 313416, 3154311, 9834802, 5123383, 7112507, 12796921, 35055832, 19867834, 56610708, 906334841, 561210372
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.

Links

Crossrefs

Cf. A102111-A102124.

Programs

  • Maple
    R:= n-> (s-> parse(cat(s[-i]$i=1..length(s))))(""||n):
a:= proc(n) option remember; `if`(n<3, binomial(n,2),
      R(R(a(n-1)) + R(a(n-2)) + R(a(n-3))))
    end:
seq(a(n), n=0..50);  # Alois P. Heinz, Jun 18 2014
  • Mathematica
    R[n_]:=FromDigits[Reverse[IntegerDigits[n]]];Clear[a];a[0]=0;a[1]=0;a[2]=1;a [n_]:=a[n]=R[R[a[n-1]]+R[a[n-2]]+R[a[n-3]]];Table[a[n], {n, 0, 40}]
rev[n_]:=FromDigits[Reverse[IntegerDigits[n]]]; nxt[{a_, b_, c_}] := {b, c, rev[rev[a] + rev[b] + rev[c]]}; Transpose[NestList[nxt,{0,0,1},40]][[1]] (* Harvey P. Dale, Mar 20 2015 *)
nxt[{a_,b_,c_}]:=With[{ir=IntegerReverse},{b,c,ir[ir[a]+ir[b]+ir[c]]}]; NestList[nxt,{0,0,1},40][[;;,1]] (* Harvey P. Dale, Jul 22 2025 *)

Formula

a(n) = A004086(A102117(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.

Links

Crossrefs

Cf. A102111, A102112, A102113, A102114, A102115, A102116, A102117, A102119, A102120, A102121, A102122, A102123, A102124, A102125.

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.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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