A133980 Home primes of semiprimes (A001358).

23, 37, 211, 223, 229, 241, 271, 283, 311, 313, 317, 331, 337, 347, 353, 359, 367, 373, 379, 383, 389, 397, 523, 541, 547, 571, 719, 743, 761, 773, 797, 1117, 1123, 1129, 1153, 1171, 1319, 1361, 1367, 1373, 1723, 1741, 1747, 1753, 1759, 1783, 1789, 1931

Offset: 1

Author

Jonathan Vos Post & Robert G. Wilson v, Oct 01 2007, Oct 06 2007

Keywords

• nonn
• base

Comments

Not the same as A133957.

Number of terms < 10^n: 0, 2, 31, 223, 1638, 11752, 89918, ....

Crossrefs

Cf. A001358, A133955, A133957.

Programs

Mathematica

lst = {}; semiPrimeQ[x_] := Plus @@ Last /@ FactorInteger@x == 2; f[n_] := FromDigits@ Flatten[IntegerDigits@ Table[ #[[1]], {#[[2]]}] & /@ FactorInteger@n, 2]; h[n_] := NestWhileList[ f@# &, n, ! PrimeQ@# &, 1, 6];