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

1,1

Comments

Not the same as A133957.

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

Links

Table of n, a(n) for n=1..48.

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];

Crossrefs

Cf. A001358, A133955, A133957.

Sequence in context: A140442 A078731 A133957 * A090312 A089782 A113893

Adjacent sequences: A133977 A133978 A133979 * A133981 A133982 A133983

Keyword

nonn,base

Author

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

Status

approved