A274700 Numbers k such that 7*10^k + 37 is prime.

1, 7, 15, 21, 91, 325, 465, 853, 76717

Offset: 1

Author

Vincenzo Librandi, Jul 04 2016

Keywords

• nonn
• more

Comments

All terms are odd because 7*(9*11+1)^n + 37 is divisible by 11.

a(10) > 10^5. - Michael S. Branicky, Apr 30 2025

Examples

			1 is in this sequence because 7*10 + 37 = 107 is prime.
3 is not in the sequence because 7*10^3 + 37 = 31*227.
Initial terms and associated primes:
  a(1) =  1: 107;
  a(2) =  7: 70000037;
  a(3) = 15: 7000000000000037;
  a(4) = 21: 7000000000000000000037;
  etc.
		

Crossrefs

Cf. similar sequences listed in A274676.

Programs

Magma

[n: n in [1..400] | IsPrime(7*10^n+37)];

Mathematica

Select[Range[0, 3000], PrimeQ[7 10^# + 37] &]

PARI

lista(nn) = for(n=1, nn, if(ispseudoprime(7*10^n+37), print1(n, ", "))); \\ Altug Alkan, Jul 05 2016

Extensions

Edited by Bruno Berselli, Jul 05 2016

a(9) from Michael S. Branicky, Apr 28 2025