login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A152006 A Fernandez expansion of the extended primes ( primes plus {0,1}): f(n)=If[n < 2, n, Prime[n - 1]]; p(x,n)=Product[1 + f(m)*x^m, {m, 0, n}];a(n)=coefficients(p(x,n). 0
1, 1, 2, 5, 8, 18, 34, 63, 102, 203, 336, 589, 999, 1675, 2799, 4768, 7561, 12224, 20513, 31724, 51621, 81976, 128560, 199192, 312536, 482806, 744847, 1147952, 1755931, 2649474, 4051413, 6069450, 9105323, 13747364, 20335077, 30508629, 45198631 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

The n=100 ratio of this extension is:1.3307144309558037. The ordinary definition gives:1.3485468888430188. Maybe I should comment that my Mathematica procedure gives a different result for A147557 than the one in the OEIS.

LINKS

Table of n, a(n) for n=0..36.

FORMULA

f(n)=If[n < 2, n, Prime[n - 1]]; p(x,n)=Product[1 + f(m)*x^m, {m, 0, n}];a(n)=coefficients(p(x,n).

MATHEMATICA

Clear[f, P, n]; f[n_] = If[n < 2, n, Prime[n - 1]]; P[x_, n_] := P[x, n] = Product[1 + f[m]*x^m, {m, 0, n}]; Length[CoefficientList[ExpandAll[P[x, 99]], x]]; a1 = CoefficientList[ExpandAll[P[x, 99]], x]; a2 = CoefficientList[ExpandAll[P[x, 100]], x]; a = Sum[If[a1[[n]] - a2[[n]] == 0, 1, 0], {n, 1, 4951}]; Table[a2[[n]], {n, 1, 100}]

CROSSREFS

Cf. A147557.

Sequence in context: A063675 A000943 A304966 * A271619 A197211 A256723

Adjacent sequences:  A152003 A152004 A152005 * A152007 A152008 A152009

KEYWORD

nonn

AUTHOR

Roger L. Bagula, Nov 19 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 18 22:08 EDT 2019. Contains 326109 sequences. (Running on oeis4.)