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.

A211964 Right triangle from the snowflake (or E-toothpick) structure of A161330 (see Comments lines for definition).

Original entry on oeis.org

0, 1, 2, 3, 5, 6, 8, 10, 12, 15, 17, 20, 24, 25, 27, 29, 32, 37, 40, 47, 51, 56, 63, 67, 73, 80, 82, 86, 90, 95, 103, 109, 120, 128, 136, 145, 151, 158, 166, 174, 182, 187, 193, 203, 210, 221, 232, 241, 250, 262, 271, 285, 294, 304, 318, 329, 343, 353, 362, 371
Offset: 0

Views

Author

Omar E. Pol, Dec 17 2012

Keywords

Comments

If n >> 1 the structure looks like a right triangle, which is essentially half of one of the six wedges of the E-toothpick (or snowflake) structure of A161330. The sequence gives the number of E-toothpicks in the structure after n stages. A211976 (the first differences) gives the number added at the n-th stage.

Links

Crossrefs

Cf. A139250, A161328, A161330, A213360, A213366, A211976, A220478.

Formula

a(n) = (((A161330(n+1) - 2)/6) + n)/2.
a(n) = A220478(n)/2. - Omar E. Pol, Feb 19 2012

A213512 Minimal of max(m,k) (m>=1,k>=0) such that (2*n-1)!!/m+2^k is prime.

Original entry on oeis.org

1, 1, 1, 1, 1, 2, 3, 3, 2, 3, 1, 1, 3, 1, 2, 4, 5, 5, 5, 2, 3, 2, 4, 4, 7, 5, 4, 7, 1, 9, 6, 3, 6, 5, 13, 10, 2, 1, 7, 3, 6, 5, 5, 5, 9, 3, 2, 5, 9, 7, 11, 1, 3, 5, 10, 5, 7, 3, 3, 5, 9, 4, 5, 11, 8, 5, 9, 8, 11, 9, 9, 13, 9, 11, 11, 9, 5, 3, 11, 11, 3, 7, 3, 9, 1, 10, 7, 9, 3, 7, 7, 11, 9, 6, 9, 16, 5, 6, 9, 5, 9, 15, 11, 12, 3, 19, 7, 7, 3, 1, 19, 7, 9, 11, 4, 19, 5, 9, 7, 11, 13, 11, 1, 7, 15, 7, 15, 18, 11, 7, 5, 19, 15, 12, 7, 19, 14, 9, 7, 11, 3, 13, 10, 13, 16, 11, 9, 11, 7, 3
Offset: 1

Views

Author

Vladimir Shevelev, Feb 15 2013

Keywords

Crossrefs

Cf. A212281, A212282, A212321, A212636, A212637, A212648, A213366.

Programs

  • PARI
    a(n)=my(m=-1,P=prod(i=2,n,2*i-1)); while(m+=2, for(k=m-2,m-1, forstep(M=1,m-2,2, if(ispseudoprime(P/M+2^k),return(k)))); for(k=0,m, if(ispseudoprime(P/m+2^k),return(m)))) \\ Charles R Greathouse IV, Feb 27 2013

Extensions

Terms beginning with a(6) were calculated by Peter J. C. Moses.
Showing 1-2 of 2 results.

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

Content is available under The OEIS End-User License Agreement.