A213019 Largest n-digit right-truncatable semiprime.

9, 95, 959, 9599, 95999, 959999, 9599999, 95999987, 959999879, 9599998799, 95999987999, 959999879999, 9599998791827, 95999987918279, 959999879182793, 9599998791715333, 95999987917153339, 959999879171533399, 9599998791715333999, 95999987917153339993

Offset: 1

Author

Hugo Pfoertner, Jun 27 2012

Keywords

• nonn
• base
• fini
• full

Comments

For the definition of a right-truncatable semiprime, see A213017. The largest possible right-truncatable semiprime a(38) = A085733(56076) = 95861957783594714393831931415189937897, found by S.S. Gupta, is the last term of this sequence.

Examples

			a(1) = 9 = 3*3
a(2) = 95 = 5*19 and none of 96, 97, 98, 99 semiprime
a(3) = 959 = 7*137
a(4) = 9599 = 29*331
a(5) = 95999 = 17*5647
a(6) = 959999 = 643*1493
a(7) = 9599999 = 1019*9421
a(8) = 95999987 = 7349*13063, 9599998 = 2*4799999 and none of 95999988 ... 95999999 semiprime
		

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..38 (all terms)
• Shyam Sunder Gupta, The largest right-truncatable semiprime, Prime Curios.

Crossrefs

Cf. A001358, A085733, A213017, A213018.