A185999 Automorphic semiprimes: semiprimes, sp, such that sp is the k-th semiprime and sp ends in k.
291, 24502749, 36627829, 3547310731, 4721984179, 461808766011
Offset: 1
Programs
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Mathematica
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}]
Extensions
a(6) from Donovan Johnson, Mar 03 2011
Comments