A263349 a(n) = smallest number > a(n-1) such that a(n-1) + a(n) is a semiprime (A001358), a(1)=1.

1, 3, 6, 8, 13, 20, 26, 29, 33, 36, 38, 39, 43, 44, 47, 48, 58, 60, 61, 62, 67, 74, 81, 85, 92, 93, 94, 100, 101, 102, 103, 106, 107, 108, 109, 110, 111, 115, 120, 127, 132, 133, 134, 140, 147, 148, 150, 151, 152, 153, 156, 158, 161, 162, 164, 165

Offset: 1

Author

Zak Seidov, Oct 15 2015

Keywords

• nonn

Comments

Similar sequences with any other initial a(1) will eventually merge with case a(1)=1.

Examples

			1 + 3 = 4 = 2*2, 3 + 6 = 9 = 3*3, 6 + 8 = 14 = 2*7, etc.
		

Crossrefs

Cf. A001358, A243625.

Programs

Mathematica

s={a=1};Do[k=a+1;While[PrimeOmega[a+k]!=2,k++];AppendTo[s,a=k],{100}];s

PARI

lista(nn) = {print1(a = 1, ", "); for (k=1, nn, na = a+1; while (bigomega(a+na) != 2, na++); a = na; print1(a, ", "););} \\ Michel Marcus, Oct 17 2015