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A068674 Numbers which yield primes when a 3 is prefixed or appended. 11
1, 7, 11, 17, 31, 37, 59, 67, 73, 109, 119, 121, 137, 169, 187, 191, 221, 229, 259, 271, 331, 343, 359, 361, 373, 407, 413, 449, 467, 499, 511, 527, 533, 539, 541, 557, 581, 607, 613, 617, 637, 673, 701, 719, 733, 739, 767, 779, 793, 823, 851, 889, 917, 929 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

73 is a term as both 373 and 733 are primes.

MAPLE

i := 0:for k from 1 to 3200 do if(isprime(3+10*k) and isprime(k+10^(ceil(evalf(log(k+1)/log(10))))*3)) then s[i] := k; i := i+1; end if; end do:q := seq(s[j], j=0..i-1);

MATHEMATICA

Select[Range[930], Union[PrimeQ[FromDigits/@{Append[(x=IntegerDigits[#]), 3], Prepend[x, 3]}]]=={True} &] (* Jayanta Basu, May 20 2013 *)

CROSSREFS

Cf. A068673.

Sequence in context: A174360 A320384 A019418 * A156112 A158594 A215419

Adjacent sequences:  A068671 A068672 A068673 * A068675 A068676 A068677

KEYWORD

base,easy,nonn

AUTHOR

Amarnath Murthy, Mar 02 2002

EXTENSIONS

More terms from Sascha Kurz, Mar 17 2002

STATUS

approved

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Last modified January 22 19:16 EST 2020. Contains 331153 sequences. (Running on oeis4.)