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A218209 Number of n-digit primes that are of the form (k-2)^2 + (k-1)^2 + k^2 4
2, 1, 3, 4, 12, 31, 86, 230, 681, 1934, 5634, 15772 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..12.

FORMULA

a(n) = A218210(n) - A218210(n-1)

MATHEMATICA

n = -1; Table[cnt = 0; While[n++; p = 3*n^2 + 2; p < 10^e, If[PrimeQ[p], cnt++]]; n--; cnt, {e, 10}] (* T. D. Noe, Oct 23 2012 *)

Table[Count[Table[Total[Range[n, n+2]^2], {n, -1, 600000}], _?(PrimeQ[#] && IntegerLength[#]==k&)], {k, 12}] (* Harvey P. Dale, Oct 17 2016 *)

CROSSREFS

Cf. A027863, A027864, A218207, A218210, A218211.

Sequence in context: A052950 A086851 A001054 * A141487 A217103 A099866

Adjacent sequences:  A218206 A218207 A218208 * A218210 A218211 A218212

KEYWORD

nonn,base

AUTHOR

Martin Renner, Oct 23 2012

STATUS

approved

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Last modified August 11 23:45 EDT 2020. Contains 336434 sequences. (Running on oeis4.)