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A235689
Semiprimes which remain semiprimes when the leftmost and rightmost digits are removed.
2
141, 142, 143, 145, 146, 161, 166, 169, 194, 247, 249, 262, 265, 267, 291, 295, 298, 299, 341, 346, 361, 362, 365, 391, 393, 394, 395, 398, 445, 446, 447, 466, 469, 493, 497, 542, 543, 545, 562, 565, 566, 591, 597, 649, 662, 667, 669, 694, 695, 697, 698, 699
OFFSET
1,1
EXAMPLE
169 = 13^2 is in the sequence because 6 = 2*3.
MATHEMATICA
Select[Range[100, 700], PrimeOmega[#]==PrimeOmega[FromDigits[ Rest[ Most[ IntegerDigits[ #]]]]] ==2&] (* Harvey P. Dale, Nov 22 2018 *)
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
delleft(a) = my(b, c); b=#Str(a); c=a\(10^(b-1)); a-c*(10^(b-1))
issemiprime(n) = n>0 && bigomega(n)==2
t=list(700); for(n=1, #t, if(issemiprime(delleft(t[n]\10)), print1(t[n], ", ")))
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Colin Barker, Jan 14 2014
STATUS
approved