OFFSET
1,1
REFERENCES
From a puzzle proposed by Marc LeBrun.
FORMULA
Sum_{n>=1} 1/a(n) = -9/10 + Product_{k>=1} (1+1/(prime(k)*prime(k+4)-1)) = 0.2602421684... . - Amiram Eldar, Sep 19 2023
MATHEMATICA
f[p_, e_] := NextPrime[p]^e * NextPrime[p, 3]^e; a[1] = 10; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 19 2023 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
EXTENSIONS
More terms from David W. Wilson
STATUS
approved