A235687 Semiprimes which remain semiprimes when the rightmost digit is removed.

46, 49, 62, 65, 69, 91, 93, 94, 95, 106, 141, 142, 143, 145, 146, 155, 158, 159, 213, 214, 215, 217, 218, 219, 221, 226, 253, 254, 259, 262, 265, 267, 334, 335, 339, 341, 346, 355, 358, 381, 382, 386, 391, 393, 394, 395, 398, 466, 469, 493, 497, 511, 514

Offset

1,1

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Example

514 is in the sequence because 51 = 3*17.

Mathematica

Select[Range[600], PrimeOmega[#]==2==PrimeOmega[FromDigits[ Most[ IntegerDigits[ #]]]]&] (* Harvey P. Dale, Oct 02 2014 *)
Select[Range[600], PrimeOmega[#]==PrimeOmega[Quotient[#, 10]]==2&] (* Harvey P. Dale, Mar 18 2023 *)

Prog

(PARI)
list(lim)=my(v=List(), t); forprime(p=2, sqrt(lim), t=p; forprime(q=p, lim\t, listput(v, t*q))); vecsort(Vec(v)) \\ From A001358
issemiprime(n) = n>0 && bigomega(n)==2
t=list(1000); for(n=1, #t, if(issemiprime(t[n]\10), print1(t[n], ", ")))

Crossrefs

Cf. A235688, A235689.

Cf. A227919, A227916, A069686.

Sequence in context: A282465 A098194 A181460 * A365009 A321046 A269671

Adjacent sequences: A235684 A235685 A235686 * A235688 A235689 A235690

Keyword

nonn,base

Author

Colin Barker, Jan 14 2014

Status

approved