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.

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A064749 a(n) = n*11^n + 1.

Original entry on oeis.org

1, 12, 243, 3994, 58565, 805256, 10629367, 136410198, 1714871049, 21221529220, 259374246011, 3138428376722, 37661140520653, 448795257871104, 5316497670165375, 62658722541234766, 735195677817154577, 8592599484487994108, 100078511642860166659, 1162022718519876379530
Offset: 0

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Author

N. J. A. Sloane, Oct 19 2001

Keywords

Crossrefs

For a(n)=n*k^n+1: A000012 (k=0), A000027(n+1) (k=1), A002064 (k=2), A050914 (k=3), A050915 (k=4), A050916 (k=5), A050917 (k=6), A050919 (k=7), A064746 (k=8), A064747 (k=9), A064748 (k=10), this sequence (k=11), A064750 (k=12).
Cf. A064757.

Programs

  • Magma
    [n*11^n+1: n in [0..20]]; // Vincenzo Librandi, Sep 16 2011
  • Maple
    k:= 11; f:= gfun:-rectoproc({-1 - (k-1)*n + k*n*a(n-1) - (n-1)*a(n) = 0, a(0) = 1, a(1) = k+1}, a(n), remember): map(f, [$0..20]); # Georg Fischer, Feb 19 2021

Formula

a(n) = A064757(n) + 2 for n>=1. - Georg Fischer, Feb 19 2021
G.f.: -(110*x^2-11*x+1)/((x-1)*(11*x-1)^2). - Alois P. Heinz, Feb 19 2021
From Elmo R. Oliveira, May 03 2025: (Start)
E.g.f.: exp(x)*(1 + 11*x*exp(10*x)).
a(n) = 23*a(n-1) - 143*a(n-2) + 121*a(n-3). (End)

A242270 Numbers k such that k*7^k+1 is semiprime.

Original entry on oeis.org

6, 8, 10, 14, 15, 60, 90, 114, 118, 204, 350, 390
Offset: 1

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Author

Vincenzo Librandi, May 10 2014

Keywords

Comments

The semiprimes of this form are: 705895, 46118409, 2824752491, 9495123019887, 71213422649146, ...
a(13) >= 720. - Kevin P. Thompson, Apr 20 2022

Crossrefs

Cf. similar sequences listed in A242203.

Programs

  • Magma
    IsSemiprime:=func; [n: n in [1..80] | IsSemiprime(s) where s is n*7^n+1];
    
  • Mathematica
    Select[Range[80], PrimeOmega[# 7^# + 1] == 2 &]
  • PARI
    is(k) = bigomega(k*7^k+1)==2;
    for(k=0,120,if(k%4!=1,if(is(k),print1(k, ", ")))); \\ Jinyuan Wang, Apr 07 2019

Extensions

a(7)-a(9) from Jinyuan Wang, Apr 07 2019
a(10)-a(12) from Kevin P. Thompson, Apr 20 2022
Showing 1-2 of 2 results.