A190664 Least semiprime whose prime factors differ by 2*prime(n).

21, 55, 39, 51, 203, 87, 111, 123, 371, 183, 335, 395, 623, 267, 291, 327, 1703, 635, 411, 1043, 447, 815, 1211, 543, 591, 7223, 1055, 2951, 1115, 687, 771, 1883, 831, 843, 4043, 1535, 951, 1655, 1011, 1047, 12059, 1835, 2723, 1167, 1191, 1203, 4763, 1347

Offset: 1

Author

Michel Lagneau, May 16 2011

Keywords

• nonn

Examples

			a(5) = 203 because 203 = 7*29, and 29 - 7 = 22 = 2*11 = 2*prime(5).
		

Crossrefs

Cf. A073703, A073704.

Programs

Mathematica

f[n_] := Block[{p=3}, While[! PrimeQ[p+2*Prime[n]], p=NextPrime[p]]; p*(p+2*Prime[n])]; Table[f[n], {n, 1, 60}]

Formula

a(n) = A073703(n) * A073704(n).