A254718 a(n) is the least semiprime having a(n-1) as a substring, a(1)=4.

4, 14, 141, 1141, 11141, 111413, 1111413, 11114137, 111114137, 1111141373, 11111141373, 111111413737, 1111114137373, 11111141373734, 1111114137373402, 11111141373734023, 111111413737340234, 11111114137373402349, 111111114137373402349, 1111111141373734023499

Offset: 1

Author

Zak Seidov, Feb 06 2015

Keywords

• nonn
• base

Examples

			4=2*2, 14=2*7, 141=3*47, 1141=7*163, 11141=13*857, 111413=43*2591, 1111413=3*370471, 11114137=47*236471, 111114137=31*3584327, 1111141373=1051*1057223.
		

Links

• Jon E. Schoenfield, Table of n, a(n) for n = 1..71
• Jon E. Schoenfield, Terms and factors for n = 1..71
• Jon E. Schoenfield, Terms and factors for n = 1..71 and tentative additional terms through n=84

Crossrefs

Cf. A001358, A030456.

Extensions

a(11)-a(20) from Jon E. Schoenfield, Feb 19 2015