A205529 -id:A205529 - cp's OEIS frontend

A205530 Composite numbers n with k digits such that each sum of 1 to k digits of n is substring of n.

4, 6, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 910, 1000, 1090, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 9010, 9100, 10000, 10090, 10900, 20000, 30000, 40000, 50000, 60000, 70000, 80000, 90000, 90010, 90100, 91000

Offset: 1

Jaroslav Krizek, Jan 28 2012

Complement of A205529 with respect to A202272.

			910 is in sequence because all possible sums of digits 0, 1, 1, 9, 9, 10, 10 are substrings of 910.

Cf. A205529, A202272.

A280828 Numbers k of the form 2*10^m + 2 such that 10^k + 9 is prime.

Original entry on oeis.org

4, 22, 202

Offset: 1

Sergey Pavlov, Jan 08 2017

Let k=2*10^(n-1)+2, then a(n)=10^k+9. For all k>4, k is a term of A058441.
The only known terms from A088275 (Numbers n such that 10^n + 9 is prime) that are of the form 2*10^j + 2 are 4, 22, and 202; given the lower bound given for that sequence's next term, a(4) >= 200002. - Jon E. Schoenfield, Jan 11 2017
For n<4, let k=a(n) and p=(10^k-9)/10^(k/2)+3=10^(k/2)+3, then p is prime. - Sergey Pavlov, Jan 13 2017

			For n=1, a(1)=4 and 10^4 + 9 is prime.

Cf. A043037, A058441, A088275, A144249, A205529.

Numbers k of the form 2*10^m + 2 such that 10^k + 9 is prime.

cp's OEIS Frontend

A205530 Composite numbers n with k digits such that each sum of 1 to k digits of n is substring of n.

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