1,1

Analogy, this sequence is to semiprimes (A001358) as A046883 is to the primes (A000040) or as A035383 is to the squares (A000290) among many others.

Table of n, a(n) for n=1..6.

Index entries for sequences related to automorphic numbers

nextSemiPrime[n_] := Block[{k = n + 1}, While[ Plus @@ Last /@ FactorInteger@ k != 2, k++]; k]; c = 1; k = 4; lst = {}; While[k < 8100000000, If[ Mod[k, 10^Floor[1 + Log10@ c]] == c, AppendTo[lst, k]; Print[{c, k}]]; c++; k = nextSemiPrime@ k]; lst

These terms can be crosschecked by: SemiPrimePi[n_] := Sum[ PrimePi[n/Prime@ i] -i + 1, {i, PrimePi@ Sqrt@ n}]

Cf. A001358, A046883, A046883, A186000.

Sequence in context: A158254 A088892 A098248 * A048956 A043439 A236049

Adjacent sequences: A185996 A185997 A185998 * A186000 A186001 A186002

hard,nonn,base

Jonathan Vos Post & Robert G. Wilson v, Feb 24 2011

a(6) from Donovan Johnson, Mar 03 2011

approved