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 1-2 of 2 results.

A099017 Numbers k such that 4*10^k + 6*R_k + 1 is prime, where R_k = 11...1 is the repunit (A002275) of length k.

Original entry on oeis.org

0, 1, 2, 6, 10, 12, 13, 22, 32, 46, 61, 68, 90, 110, 652, 1608, 1904, 2003, 3038, 3086, 9580, 9698, 10639, 14461
Offset: 1

Views

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Nov 13 2004

Keywords

Comments

Also numbers k such that (14*10^k + 1)/3 is prime.
a(25) > 2*10^5. - Robert Price, Jul 11 2015

Examples

			n = 1, 2, 6 are members since 47, 467, 4666667 are primes.

Links

Crossrefs

Cf. A002275, A099005, A098959, A101731.

Programs

  • Mathematica
    Do[ If[ PrimeQ[(14*10^n + 1)/3], Print[n]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 17 2005 *)

Formula

a(n) = A101731(n-1) + 1, for n>1.

Extensions

a(15)-a(22) from Robert G. Wilson v, Jan 17 2005
a(23)-a(24) from Kamada data by Robert Price, Dec 08 2010
Prepended a(1)=0 by Robert Price, Jul 11 2015

A101964 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) + 33 for n > 0.

Original entry on oeis.org

0, 1, 2, 4, 5, 6, 10, 20, 29, 67, 72, 168, 175, 344, 822, 1020, 1190, 2072, 2754, 10716, 14672, 16753, 17605, 81028, 120850, 167964, 200407
Offset: 1

Views

Author

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004

Keywords

Comments

Numbers n such that (240*10^n - 33)/9 is prime.
Numbers n such that digit 2 followed by n >= 0 occurrences of digit 6 followed by digit 3 is prime.
Numbers corresponding to terms <= 822 are certified primes.
a(28) > 3*10^5. - Robert Price, Jul 13 2023

Examples

			263 is prime, hence 1 is a term.

References

  • Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

Links

Crossrefs

Cf. A000533, A002275, A098959.

Programs

  • PARI
    a=23;for(n=0,1500,if(isprime(a),print1(n,","));a=10*a+33)
  • PARI
    for(n=0,1500,if(isprime((240*10^n-33)/9),print1(n,",")))

Formula

a(n) = A098959(n) - 1.

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
a(24) derived from A098959 by Robert Price, Jan 17 2015
a(25)-a(27) derived from A098959 by Robert Price, Jul 13 2023
Showing 1-2 of 2 results.

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

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