A122506 A symmetrical triangular array based on A018805 constructed by hand by adding ones between the primes and making the result symmetrical.

1, 1, 3, 1, 1, 3, 1, 7, 1, 3, 1, 1, 3, 1, 7, 1, 11, 1, 7, 1, 3, 1, 1, 3, 1, 7, 1, 11, 1, 19, 1, 11, 1, 7, 1, 3, 1, 1, 3, 1, 7, 1, 11, 1, 19, 1, 23, 1, 19, 1, 11, 1, 7, 1, 3, 1

Offset

1,3

Comments

The first two terms past one come from removing the zeros from coefficients here: Expand[(x^2 - x - 1)*(x^2 + x - 1)] Abs[CoefficientList[1 - 3 x^2 + x^4, x]] {1, 0, 3, 0, 1} Expand[(x^3 - 2*x^2 - x + 1)*(x^3 - x^2 - 2*x + 1)] Abs[CoefficientList[1 - 3 x - x^2 + 7 x^3 - x^4 - 3 x^5 + x^6, x]] {1, 3, 1, 7, 1, 3, 1}

Links

Table of n, a(n) for n=1..56.

Example

1
1, 3, 1
1, 3, 1, 7, 1, 3, 1
1, 3, 1, 7, 1, 11, 1, 7, 1, 3, 1
1, 3, 1, 7, 1, 11, 1, 19, 1, 11, 1, 7, 1, 3, 1
1, 3, 1, 7, 1, 11, 1, 19, 1, 23, 1, 19, 1, 11, 1, 7, 1, 3, 1

Crossrefs

Cf. A018805.

Sequence in context: A131327 A355899 A341050 * A375286 A010274 A137728

Adjacent sequences: A122503 A122504 A122505 * A122507 A122508 A122509

Keyword

nonn,uned,tabl

Author

Roger L. Bagula, Sep 15 2006

Status

approved