A245382 Primes whose product of digits is a semiprime.

19, 23, 37, 41, 53, 61, 73, 127, 137, 157, 173, 191, 251, 271, 313, 317, 331, 521, 571, 751, 911, 1123, 1153, 1213, 1217, 1231, 1321, 1531, 1571, 1721, 2113, 2131, 2311, 2711, 3121, 3511, 4111, 5113, 5171, 5711, 7121, 7151, 7211, 11119, 11161, 11173, 11177, 11213

Offset

1,1

Comments

The linked table includes probable primes. - Jens Kruse Andersen, Jul 21 2014

Links

K. D. Bajpai and Jens Kruse Andersen, Table of n, a(n) for n = 1..10000 (first 370 terms from K. D. Bajpai)

Example

137 is prime. 1 * 3 * 7 = 21 = 3 * 7, which is semiprime.
251 is prime. 2 * 5 * 1 = 10 = 2 * 5, which is semiprime.

Mathematica

Select[Prime[Range[1000]], PrimeOmega[(Times @@ IntegerDigits[#])] == 2 &]

Prog

(PARI) f(n, b, d) = if(d, for(i=1, 9, if(b+bigomega(i)<=2, f(10*n+i, b+bigomega(i), d-1))), if(b==2 && isprime(n), print1(n", ")))
for(d=1, 8, f(0, 0, d)) \\ f(0, 0, d) prints d-digit terms. Jens Kruse Andersen, Jul 21 2014

Crossrefs

Cf. A000040, A001358, A046703, A007954.

Sequence in context: A245585 A343741 A060269 * A075585 A052030 A045297

Adjacent sequences: A245379 A245380 A245381 * A245383 A245384 A245385

Keyword

nonn,base

Author

K. D. Bajpai, Jul 20 2014

Status

approved