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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

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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