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A157173 Primes with sum of smallest digit and final digit is a prime. 1
11, 23, 29, 31, 41, 47, 61, 67, 71, 89, 103, 107, 131, 151, 181, 191, 211, 223, 229, 233, 239, 241, 251, 263, 269, 271, 281, 283, 293, 307, 311, 331, 421, 431, 449, 457, 461, 467, 479, 487, 491, 499, 503, 521, 523, 541, 547, 571, 607, 631, 641, 647, 661, 677 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

a(n) ~ (4/3) n log n since almost all primes not ending in 1 are in this sequence, and only o(x^0.96) primes ending in 1 are in this sequence. - Charles R Greathouse IV, Jan 02 2013

EXAMPLE

11(1+1=2=prime), 23(2+3=5=prime), 29(2+9=11=prime), 31(1+1=2=prime), etc.

MATHEMATICA

sldpQ[n_]:=Module[{idn=IntegerDigits[n]}, PrimeQ[Min[idn]+Last[idn]]]; Select[Prime[Range[150]], sldpQ] (* Harvey P. Dale, May 09 2012 *)

PROG

(PARI) is(n)=my(d=digits(n)); isprime(vecmin(d)+d[#d]) && isprime(n) \\ Charles R Greathouse IV, Jan 02 2013

CROSSREFS

Cf. A000040.

Sequence in context: A205714 A061752 A122259 * A257318 A090423 A232085

Adjacent sequences:  A157170 A157171 A157172 * A157174 A157175 A157176

KEYWORD

nonn,base

AUTHOR

Juri-Stepan Gerasimov, Feb 24 2009

EXTENSIONS

Second 151 replaced by 251, 643 removed by R. J. Mathar, Feb 26 2009

STATUS

approved

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Last modified February 19 13:25 EST 2020. Contains 332044 sequences. (Running on oeis4.)