A072348 Number of primes whose decimal representation has the form rns where r and s are single digits.

15, 13, 13, 15, 14, 16, 15, 15, 13, 14, 11, 10, 12, 9, 5, 12, 10, 10, 8, 8, 12, 13, 13, 13, 9, 11, 8, 12, 12, 13, 11, 10, 11, 10, 11, 9, 9, 11, 10, 12, 5, 11, 11, 12, 12, 11, 12, 10, 11, 9, 7, 10, 14, 11, 14, 11, 9, 10, 10, 11, 11, 8, 12, 10, 12, 12, 11, 13, 11, 15, 11, 11, 10, 12

Offset

0,1

Comments

a(2437) = 0 and a(n)>0 for n<2437, see A069691(2437) = 0;

a(1660) = 1 and a(n)>1 for n<1660, A069691(1660) = 216607;

a(n) <= 16 for all n, a(5) = 16, conjecture: a(n)<16 for n>5.

Links

Table of n, a(n) for n=0..73.

Example

The 16 prime sandwiches for n=5: 151, 157, 251, 257, 353, 359, 457, 557, 653, 659, 751, 757, 853, 857, 859 and 953.

Crossrefs

Sequence in context: A338069 A195533 A299315 * A317422 A129786 A104056

Adjacent sequences: A072345 A072346 A072347 * A072349 A072350 A072351

Keyword

nonn,base

Author

Reinhard Zumkeller, Jul 17 2002

Extensions

Offset corrected by Sean A. Irvine, Sep 24 2024

Status

approved