login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A320584 Numbers whose first digit is prime. 1
2, 3, 5, 7, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..62.

MATHEMATICA

Select[Range@ 218, PrimeQ@ First@ IntegerDigits@ # &] (* Michael De Vlieger, Nov 05 2018 *)

PROG

(PARI) isok(n) = isprime(digits(n)[1]); \\ Michel Marcus, Oct 17 2018

(PARI) a(n) = n--; my (w=1); while (n >= 4*w, n -= 4*w; w*=10); w*prime(1+n\w) + (n%w) \\ Rémy Sigrist, Nov 16 2018

CROSSREFS

Supersequence of A320585 (primes whose first digit is prime).

Cf. A000030, A000040.

Sequence in context: A048420 A048405 A110457 * A209191 A162948 A024768

Adjacent sequences:  A320581 A320582 A320583 * A320585 A320586 A320587

KEYWORD

nonn,base

AUTHOR

Kritsada Moomuang, Oct 16 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 12 14:35 EST 2019. Contains 329058 sequences. (Running on oeis4.)