A154507 Nonprimes formed by concatenation of the decimal digits of a nonprime and its index.

1, 12, 64, 85, 96, 128, 1510, 1611, 1812, 2013, 2114, 2215, 2416, 2517, 2618, 2820, 3021, 3222, 3424, 3525, 3626, 3827, 3928, 4029, 4230, 4431, 4532, 4633, 4834, 4935, 5036, 5137, 5238, 5439, 5540, 5742, 6044, 6245, 6346, 6447, 6548, 6649, 6850, 6951

Offset

1,2

Comments

Nonprimes of the form A141468(k)//k, where double slashes represent concatenation, sorted along increasing k.

Links

Table of n, a(n) for n=1..44.

Example

A141468(n=1)//1 = 0//1 = 1 is not prime and inserted into the sequence.
A141468(n=2)//2 = 1//2 = 12 is not prime and inserted into the sequence.
A141468(n=3)//3 = 4//3 = 43 is prime and not inserted into the sequence.

Maple

cat2 := proc(a, b) dgs := max(1, ilog10(b)+1) ; a*10^dgs+b ; end:
n := 0 ; for c from 0 to 80 do if not isprime(c) then n := n + 1 ; if not isprime(cat2(c, n)) then printf("%d, ", cat2(c, n)) ; fi; fi; od: # R. J. Mathar, Aug 03 2009

Crossrefs

Cf. A000040, A141468.

Sequence in context: A275404 A162472 A008425 * A105916 A193872 A258617

Adjacent sequences: A154504 A154505 A154506 * A154508 A154509 A154510

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jan 11 2009

Extensions

Edited by R. J. Mathar, Aug 03 2009

Status

approved