A154545 Odd nonprimes k such that the smallest digit of k + the number of smallest digits of k is prime.

1, 15, 21, 25, 27, 33, 45, 49, 51, 55, 69, 81, 91, 99, 115, 117, 119, 121, 123, 125, 129, 133, 135, 141, 143, 145, 147, 153, 155, 159, 161, 165, 169, 171, 175, 177, 183, 185, 187, 189, 195, 213, 215, 217, 219, 221, 231, 235, 237, 243, 245, 247, 249, 253, 255

Offset

1,2

Links

Jinyuan Wang, Table of n, a(n) for n = 1..10000

Example

1 is the smallest digit of 15 and it appears once, 1+1 is prime so 15 appears in the sequence; and so does 21, 51, 81, 91.

Maple

frequdig := proc(n, dig) local f, d ; f := 0 ; for d in convert(n, base, 10) do if d = dig then f :=f+1; end if; end do; f ; end proc:
A054054 := proc(n) min(op(convert(n, base, 10)) ) ; end proc:
for n from 1 to 500 by 2 do if not isprime(n) then sdg := A054054(n) ; a := sdg +frequdig(n, sdg) ; if isprime(a) then printf("%d, ", n ) ; end if; end if; end do: # R. J. Mathar, May 05 2010

Crossrefs

Cf. A054054 (smallest digit of n).

Sequence in context: A306102 A177024 A325037 * A156063 A181780 A273061

Adjacent sequences: A154542 A154543 A154544 * A154546 A154547 A154548

Keyword

nonn,base,less

Author

Juri-Stepan Gerasimov, Jan 11 2009

Extensions

Entries checked by R. J. Mathar, May 05 2010

Status

approved