A235689 -id:A235689 - cp's OEIS frontend

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

Colin Barker, Jan 14 2014

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

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

Cf. A235688, A235689.

Cf. A227919, A227916, A069686.

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 *)

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],", ")))

A235688 Semiprimes which remain semiprimes when the leftmost digit is removed.

Original entry on oeis.org

14, 26, 34, 39, 46, 49, 69, 74, 86, 94, 106, 115, 121, 122, 133, 134, 146, 155, 158, 169, 177, 185, 187, 194, 206, 209, 214, 215, 221, 226, 235, 249, 262, 265, 274, 287, 291, 295, 309, 314, 321, 326, 334, 335, 339, 346, 355, 358, 362, 365, 377, 382, 386, 391

Offset: 1

Colin Barker, Jan 14 2014

			249 is in the sequence because 49 = 7*7.

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

Cf. A235687, A235689.

Cf. A227919, A227916, A069686.

Select[Range[400],PrimeOmega[#]==PrimeOmega[Mod[#,10^(IntegerLength[ #]-1)]] == 2&] (* Harvey P. Dale, Jun 07 2017 *)

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(500); for(n=1, #t, if(issemiprime(delleft(t[n])), print1(t[n],", ")))

cp's OEIS Frontend

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

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