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A069845
Number of distinct primes obtained by inserting a 4 at all possible places in n. This includes prefixing.
10
1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 2, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 2, 0, 2, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0
OFFSET
1,19
LINKS
EXAMPLE
See the example in A069842.
MATHEMATICA
Table[ Count[ PrimeQ[ Union[ FromDigits /@ Table[ Insert[ IntegerDigits[n], 4, j], {j, 1, Floor[ Log[10, n] + 2]}]]], True], {n, 1, 105}]
PROG
(PARI) A069845(n) = { my(digs=digits(n), u=#digs, nums=Set([])); for(n=1, 1+u, nums = setunion(nums, [fromdigits(vector(1+u, i, if(i<n, digs[i], if(i>n, digs[i-1], 4))))])); #select(isprime, nums); }; \\ Antti Karttunen, Aug 23 2019
KEYWORD
base,nonn
AUTHOR
Amarnath Murthy, Apr 16 2002
EXTENSIONS
Edited and extended by Robert G. Wilson v, Apr 18 2002
STATUS
approved