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 1-3 of 3 results.

A048847 Primes formed by concatenation of first k odd numbers.

Original entry on oeis.org

13, 135791113151719, 135791113151719212325272931, 135791113151719212325272931333537394143454749515355575961636567
Offset: 1

Views

Author

N. J. A. Sloane, Charles T. Le (charlestle(AT)yahoo.com)

Keywords

Comments

The next term (a(5)) has 93 digits. - Harvey P. Dale, Mar 05 2013
a(6) has 9725 digits (see A066811(6) or A046036(6)). - Michel Marcus, Jan 31 2014

References

  • R. W. Stephan, Factors and Primes in Two Smarandache Sequences, Smarandache Notions Journal, second edition, Vol. 9, No. 1-2, 1998, 5-11.

Links

Crossrefs

Cf. A019519, A046036.

Programs

  • Mathematica
    Select[Table[FromDigits[Flatten[IntegerDigits/@Range[1,2n+1,2]]],{n,40}], PrimeQ] (* Harvey P. Dale, Mar 05 2013 *)

Extensions

Edited by Charles R Greathouse IV, Apr 23 2010

A046036 Indices of the concatenation of the first k odd numbers (A019519) which are primes.

Original entry on oeis.org

2, 10, 16, 34, 49, 2570
Offset: 1

Views

Author

Eric W. Weisstein

Keywords

Comments

No others with k <= 12000. - Eric W. Weisstein, Mar 01 2004
No others with k <= 25000. - Michael S. Branicky, Aug 28 2025

Links

Crossrefs

Cf. A019519, A048847, A066811.

Programs

Formula

a(n) = (A066811(n)+1)/2. - Michel Marcus, Jan 31 2014

A109445 Numbers k such that (concatenation of even integers through k) - 1 is a prime.

Original entry on oeis.org

4, 8, 10, 42, 452, 1014
Offset: 1

Views

Author

Ryan Propper, Aug 26 2005

Keywords

Comments

Next term is greater than 2000. All terms less than 1000 correspond to certified primes (Primo 2.2.0 beta).
Next term is greater than 20000. - Michael S. Branicky, Aug 28 2025

Examples

			4 is a term because 24 - 1 = 23 is prime.
8 is a term because 2468 - 1 = 2467 is prime.

Crossrefs

Cf. A066811.

Programs

  • Mathematica
    p = ""; Do[p = p <> ToString[2*n]; If[PrimeQ[ToExpression[p] - 1], Print[2*n]], {n, 1, 10^3}]
Showing 1-3 of 3 results.

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

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