A085776 Numbers k such that k concatenated with k+1 is a semiprime.

3, 10, 14, 17, 18, 20, 21, 26, 30, 32, 33, 38, 45, 46, 48, 53, 54, 57, 66, 70, 72, 77, 81, 84, 88, 98, 101, 105, 110, 116, 118, 122, 125, 128, 132, 140, 141, 142, 146, 152, 158, 162, 164, 170, 173, 176, 177, 178, 185, 190, 194, 198, 204, 206, 208, 210, 212, 218, 222

Offset

1,1

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000

Example

10 is a term because 1011 = 3*337.

Mathematica

Select[Range[300], PrimeOmega[FromDigits[IntegerString[#] <> IntegerString[#+1]]] == 2 &] (* Paolo Xausa, Apr 17 2024 *)

Crossrefs

Cf. A001358, A001704.

Sequence in context: A041865 A357628 A289151 * A289106 A289018 A316672

Adjacent sequences: A085773 A085774 A085775 * A085777 A085778 A085779

Keyword

base,easy,nonn

Author

Jason Earls, Jul 23 2003

Status

approved