1,1

Number of primes of the form: ... ddd3ddd2ddd1ddd0 = ddd0 * 10 ^ 0 + ddd1 * 10 ^ 3 + ddd2 * 10 ^ 6 + ddd3 * 10 ^ 9... where ddd0, ddd1, ddd2, ddd3... are prime with 3 digits. The i-th element of the sequence is the number of primes with i * 3 digits. Aproximation for the sum of the sequence up to a(k) for large values of k: sum( a(i), i =1 .. k ) = 10 ^ ( 3*k ) / ( ( 3*k )*log(10))* ( 143/1000)^(k-1).

Example: a(2) = 2753 because there are 2753 numbers of the form ddd1ddd0 with ddd0, ddd1 prime numbers i.e: 101107,101113,101149,101173,101197,101281,101293 ... 997991

Cf. A135944 A135945 A135946.

Sequence in context: A156635 A035304 A159054 this_sequence A029555 A046179 A147553

Adjacent sequences: A135943 A135944 A135945 this_sequence A135947 A135948 A135949

nonn,base,bref

Giorgio Balzarotti & Paolo P. Lava (greenblue(AT)tiscali.it), Dec 07 2007