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A073172 The value of index for composite numbers with square subscripts which are also square numbers. 1
1, 4, 9, 1024, 5621641, 10188864, 27657081, 308950929, 619113924, 904265041, 10011203136 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..11.

FORMULA

Solutions to c[x^2]=y^2, values of x^2; where c(j)=j-th composite number; See program.

EXAMPLE

a(4)=1024 corresponds to composite=1225=35.35=c(1024)=c(32.32).

MATHEMATICA

c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x] Do[s=c[n^2]; If[IntegerQ[Sqrt[s]], Print[n^2]], {n, 1, 1000000}]

CROSSREFS

Cf. A002808, A073171.

Sequence in context: A254959 A028869 A179935 * A168139 A258660 A260305

Adjacent sequences:  A073169 A073170 A073171 * A073173 A073174 A073175

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 19 2002

EXTENSIONS

a(9)-a(11) from Donovan Johnson, Jan 24 2011

STATUS

approved

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Last modified September 21 23:55 EDT 2019. Contains 327286 sequences. (Running on oeis4.)