A114521 a(n) = A008475(A114520(n)).

5, 7, 7, 11, 13, 11, 11, 19, 13, 13, 19, 17, 29, 31, 17, 23, 43, 19, 29, 31, 23, 61, 73, 41, 37, 83, 19, 47, 31, 67, 53, 103, 29, 17, 109, 37, 127, 71, 23, 139, 41, 151, 83, 31, 43, 181, 193, 131, 23, 101, 23, 199, 29, 41, 107, 19, 61, 43, 37, 113, 71, 229, 23, 67, 241

Offset

1,1

Links

Table of n, a(n) for n=1..65.

Example

24 (which is composite) is the sixth term of sequence A114520. 24 = 2^3 * 3 and 2^3 + 3 = 11 (which is prime). So a(6) = 11.

Mathematica

f[n_] := Plus @@ Power @@@ FactorInteger[n]; f /@ Select[Select[Range[500], PrimeQ[f[ # ]] &], ! PrimeQ[ # ] &] (* Ray Chandler, Dec 07 2005 *)

Prog

(PARI) A008475(n)=local(t); if(n<1, 0, t=factor(n); sum(k=1, matsize(t)[1], t[k, 1]^t[k, 2])); for(i=1, 900, if(!isprime(i)&&isprime(A008475(i)), print1(A008475(i), ", "))) (Herrgesell)

Crossrefs

Cf. A008475, A114518, A114519, A114520, A047820.

Sequence in context: A053672 A087525 A078496 * A258653 A159482 A231935

Adjacent sequences: A114518 A114519 A114520 * A114522 A114523 A114524

Keyword

nonn

Author

Leroy Quet, Dec 05 2005

Extensions

Extended by Ray Chandler and Lambert Herrgesell (zero815(AT)googlemail.com), Dec 07 2005

Status

approved